Laser processing apparatus, methods of laser-processing workpieces and related arrangements

ABSTRACT

Apparatus and techniques for laser-processing workpieces can be improved, and new functionalities can be provided. Some embodiments discussed relate to processing of workpieces in a manner resulting in enhanced accuracy, throughput, etc. Other embodiments relate to realtime Z-height measurement and, when suitable, compensation for certain Z-height deviations. Still other embodiments relate to modulation of scan patterns, beam characteristics, etc., to facilitate feature formation, avoid undesirable heat accumulation, or otherwise enhance processing throughput. A great number of other embodiments and arrangements are also detailed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a PCT National Phase in US (371) patent application claimspriority of PCT/US2016/50804, filed Sep. 8, 2016. Which claims thebenefit of U.S. Provisional Application No. 62/216,102, filed Sep. 9,2015, of U.S. Provisional Application No. 62/241,624, filed Oct. 14,2015, of U.S. Provisional Application No. 62/271,446, filed Dec. 28,2015, of U.S. Provisional Application No. 62/294,991, filed Feb. 12,2016, and of U.S. Provisional Application No. 62/366,984, filed Jul. 26,2016, each of which is incorporated by reference in its entirety.

BACKGROUND I. Technical Field

Embodiments disclosed herein relate generally to laser processingapparatus and methods for laser-processing of workpieces.

II. Discussion of the Related Art

Material ablation by pulsed light sources has been studied since theinvention of the laser. Reports in 1982 of polymers having been etchedby ultraviolet (UV) excimer laser radiation stimulated widespreadinvestigations of the process for micromachining. Since then, scientificand industrial research in this field has proliferated—mostly spurred bythe remarkably small features that can be drilled, milled, marked, andreplicated through the use of lasers. A wide variety of potentialapplications for lasers in high-tech manufacturing industries have been,and continue to be developed and implemented. For example, lasers are auseful tool for milling or drilling holes, forming trenches, etc., andforming other features in or on a wide range of materials. Thecombination of high resolution, accuracy, speed, and flexibility hasallowed laser processing to gain acceptance in many industries,including the manufacture of workpieces such as integrated circuits,hard disks, printing devices, displays, interconnects, and the like.However, trends in many industries tend to demand the formation of morefeatures, smaller features, a higher density of features, etc., thuspushing the limits of existing laser-processing technologies to processworkpieces with an acceptable level of accuracy, quality, throughput andflexibility.

SUMMARY

In one embodiment, a method of forming a via in a workpiece involvesrastering a beam axis (along which laser pulses can be directed onto theworkpiece) with respect to the workpiece, and delivering a plurality oflaser pulses to the workpiece at a plurality of spot locations.

In another embodiment, a method of forming a via in a workpiece involvesmoving a beam axis relative to the workpiece using positioner includingan AOD while directing laser pulses along a beam path that forms thebeam axis to form a via having a diameter that is less than or equal toa scanning range associated with the AOD.

In another embodiment, a method of forming a feature in a workpieceincludes moving the beam axis relative to the workpiece such that groupsof laser pulses are delivered to the workpiece along many scan linesand, for each scan line, the last laser pulse is delivered to a locationthat is closer to the boundary of the feature to be formed than alocation to which a first laser pulse was delivered.

In still another embodiment, a method of processing a workpiece includesmoving the beam axis relative to the workpiece within a scanning range,wherein an extent of the first scanning range in a first direction isless than an extent of the first scanning range in a second direction.

In yet another embodiment, an apparatus for processing a workpiece,using multiple beams of laser energy, can include first to fourth scanheads; a first stage configured to impart a first movement to the firstand third scan heads, and a second stage configured to impart a secondmovement to the first and second scan heads.

In still another embodiment, an apparatus can include multipledistributors for direct a beam of laser energy among multiple beampaths.

In another embodiment, an optics assembly, for use in an apparatus forlaser-processing a workpiece, can include a housing having an opticalinput port and an optical output port, wherein the housing includes atleast one registration feature configured to facilitate opticalalignment of a beam path within the apparatus with at least one selectedfrom the group consisting of the optical input and output ports. Theoptics assembly may further include at least two optical componentsmounted within the housing and in optical alignment with the opticalinput and output ports.

In one embodiment, an acousto-optic (AO) device can include an AO cell,an ultrasonic transducer, an absorber, and a cooling plate in thermalcontact with a face of the AO cell extending between the ultrasonictransducer and the absorber. Thermal transfer characteristics of thecooling plate can vary along a direction extending from the connectorend and the absorber end such that the cooling plate can: a) remove lessheat from a central region of the AO cell that is located relatively farfrom at least one selected from the group consisting of the connectorend and the absorber end, and b) remove relatively more heat from aperipheral region of the AO cell relatively close to at least oneselected from the group consisting of the connector end and the absorberend.

In another embodiment, a method includes driving an AOD system tomodulate a received laser pulse such that an M² factor and/or a spatialintensity profile type of the modulated laser pulse is different fromthat of the received laser pulse.

In still another embodiment, a method includes generating laser pulseshaving a wavelength in a range from 9 μm to 11 μm and deflecting a beampath along which the pulses propagate using an acousto-optic deflector(AOD) including an AO cell containing germanium.

In yet another embodiment, a method of forming a feature in a workpieceincluding an electrical conductor structure arranged in thermal contactwith a dielectric structure can include indirectly ablating theelectrical conductor structure using laser pulses having a wavelengthless than 1 μm. Another method of forming a feature in a workpiece canalso deflecting a beam of laser pulses to irradiate a plurality of spotlocations and indirectly ablate a layer of material.

In still another embodiment, a method for processing of a workpiece caninclude delivering the first and second beams of laser energy along acommon beam axis to ablate a workpiece, wherein the first beam of laserenergy has a wavelength to which at least a portion of the workpiece istransparent, and is characterized by a plurality of laser pulses havinga first pulse duration sufficiently short so as to induce nonlinearabsorption of light within the portion of the workpiece, and wherein thetiming with which laser pulses in the first beam of laser energy aregenerated is independent of the act of generating the second beam oflaser energy.

As will become evident, the present specification identifies a greatnumber of problems (e.g., associated with accuracy, quality, throughput,etc., which are difficult to overcome with conventional laser processingapparatus or conventional laser processing techniques), and details agreat number of embodiments, examples, implementations, combinations,etc., that overcome such problems, provide new or improved capabilities,and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an apparatus for processing aworkpiece, according to one embodiment.

FIG. 2 schematically illustrates a second positioner of the apparatusshown in FIG. 1, according to one embodiment.

FIG. 3 schematically illustrates second scanning ranges associated withthe second positioner shown in FIG. 2, according to some embodiments.

FIGS. 4 to 6 schematically illustrate a spatial relationship between asensing range and a second scanning range, according to someembodiments.

FIG. 7 schematically illustrates a multi-head apparatus for processing aworkpiece, according to one embodiment.

FIGS. 8 and 9 schematically illustrates top and side views of aworkpiece handling system, for use with an apparatus such as those shownin FIGS. 1 and 7, according to one embodiment.

FIG. 10 schematically illustrates a process flow associated with themulti-head apparatus shown in FIG. 7, according to one embodiment.

FIGS. 11 to 24 schematically illustrate techniques for scanning asensing range and second scanning range, according to some embodiments.

FIGS. 25 to 28 schematically illustrate techniques for scanning aprocess spot, according to some embodiments.

FIGS. 29, 29A and 29B schematically illustrate a scanning techniquefacilitating anisotropic material removal, according to one embodiment.Specifically, FIG. 29 illustrates a scan pattern overlaid on a top viewof a workpiece to be processed. FIGS. 29A and 29B schematicallyillustrate cross-sectional views of a feature formed using the scanpattern shown in FIG. 29, taken along lines XXIXA-XXIXA andXXIXB-XXIXB′, respectively.

FIGS. 30 to 32 schematically illustrate a multi-source apparatus,according to some embodiments.

FIG. 33 schematically illustrates a manner of combining beams of laserenergy in a multi-source apparatus, according to one embodiment.

FIGS. 34 to 37 schematically illustrate techniques for managing thermalloads within an AO cell, according to some embodiments.

FIG. 38 schematically illustrates a byproduct removal system, accordingto one embodiment.

DETAILED DESCRIPTION

Example embodiments are described herein with reference to theaccompanying drawings. Unless otherwise expressly stated, in thedrawings the sizes, positions, etc., of components, features, elements,etc., as well as any distances therebetween, are not necessarily toscale, but are exaggerated for clarity. In the drawings, like numbersrefer to like elements throughout. Thus, the same or similar numbers maybe described with reference to other drawings even if they are neithermentioned nor described in the corresponding drawing. Also, evenelements that are not denoted by reference numbers may be described withreference to other drawings.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. Unlessotherwise defined, all terms (including technical and scientific terms)used herein have the same meaning as commonly understood by one ofordinary skill in the art. As used herein, the singular forms “a,” “an”and “the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It should be recognized that theterms “comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. Unless otherwise specified,a range of values, when recited, includes both the upper and lowerlimits of the range, as well as any sub-ranges therebetween. Unlessindicated otherwise, terms such as “first,” “second,” etc., are onlyused to distinguish one element from another. For example, one nodecould be termed a “first node” and similarly, another node could betermed a “second node”, or vice versa.

Unless indicated otherwise, the term “about,” “thereabout,” etc., meansthat amounts, sizes, formulations, parameters, and other quantities andcharacteristics are not and need not be exact, but may be approximateand/or larger or smaller, as desired, reflecting tolerances, conversionfactors, rounding off, measurement error and the like, and other factorsknown to those of skill in the art. Spatially relative terms, such as“below,” “beneath,” “lower,” “above,” and “upper,” and the like, may beused herein for ease of description to describe one element or feature'srelationship to another element or feature, as illustrated in the FIGS.It should be recognized that the spatially relative terms are intendedto encompass different orientations in addition to the orientationdepicted in the FIGS. For example, if an object in the FIGS. is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. An object may be otherwise oriented (e.g., rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may be interpreted accordingly.

The section headings used herein are for organizational purposes onlyand, unless explicitly stated otherwise, are not to be construed aslimiting the subject matter described. It will be appreciated that manydifferent forms, embodiments and combinations are possible withoutdeviating from the spirit and teachings of this disclosure and so thisdisclosure should not be construed as limited to the example embodimentsset forth herein. Rather, these examples and embodiments are provided sothat this disclosure will be thorough and complete, and will convey thescope of the disclosure to those skilled in the art.

I. Overview

Embodiments described herein relate generally to methods and apparatusesfor laser-processing (or, more simply, “processing”) a workpiece.Generally the processing is accomplished, either in whole or in part, byirradiating the workpiece with laser radiation, to heat, melt,evaporate, ablate, crack, discolor, polish, roughen, carbonize, foam, orotherwise modify one or more properties or characteristics of one ormore materials from which the workpiece is formed (e.g., in terms ofchemical composition, atomic structure, ionic structure, molecularstructure, electronic structure, microstructure, nanostructure, density,viscosity, index of refraction, magnetic permeability, relativepermittivity, texture, color, hardness, transmissivity toelectromagnetic radiation, or the like or any combination thereof).Materials to be processed may be present at an exterior of the workpieceprior to or during processing, or may be located completely within theworkpiece (i.e., not present at an exterior of the workpiece) prior toor during processing.

Specific examples of processes that may be carried by the disclosedapparatus for laser processing include via drilling or other holeformation, cutting, perforating, welding, scribing, engraving, marking(e.g., surface marking, sub-surface marking, etc.), laser-inducedforward transfer, cleaning, bleaching, bright pixel repair (e.g., colorfilter darkening, modification of OLED material, etc.), decoating,surface texturing (e.g., roughening, smoothing, etc.), or the like orany combination thereof. Thus, one or more features on that may beformed on or within a workpiece, as a result of the processing, caninclude openings, slots, vias or other holes, grooves, trenches, scribelines, kerfs, recessed regions, conductive traces, ohmic contacts,resist patterns, human- or machine-readable indicia (e.g., comprised ofone or more regions in or on the workpiece having one or more visuallyor texturally distinguishing characteristics), or the like or anycombination thereof. Features such as openings, slots, vias, holes,etc., can have any suitable or desirable shape (e.g., circular,elliptical, square, rectangular, triangular, annular, or the like or anycombination thereof) when viewed from a top plan view. Further, featuressuch as openings, slots, vias, holes, etc., can extend completelythrough the workpiece (e.g., so as to form so-called “through vias,”“through holes,” etc.) or only partially through the workpiece (e.g., soas to form so-called “blind vias,” “blind holes,” etc.).

Workpieces that may be processed can be generically characterized beingformed of one or more metals, polymers, ceramics, composites, or anycombination thereof (e.g., whether as an alloy, compound, mixture,solution, composite, etc.). Specific examples of workpieces that may beprocessed include, panels of printed circuit boards (PCBs) (alsoreferred to herein as “PCB panels”), PCBs, flexible printed circuits(FPCs), integrated circuits (ICs), IC packages (ICPs), light-emittingdiodes (LEDs), LED packages, semiconductor wafers, electronic or opticaldevice substrates (e.g., substrates formed of Al₂O₃, AN, BeO, Cu, GaAS,GaN, Ge, InP, Si, SiO₂, SiC, Si_(1-x)Ge_(x) (where 0.0001<x<0.9999), orthe like, or any combination or alloy thereof), lead frames, lead frameblanks, articles formed of plastic, unstrengthened glass,thermally-strengthened glass, chemically-strengthened glass (e.g., viaan ion-exchange process), quartz, sapphire, plastic, silicon, etc.,components of electronic displays (e.g., substrates having formedthereon, TFTs, color filters, organic LED (OLED) arrays, quantum dot LEDarrays, or the like or any combination thereof), lenses, mirrors, screenprotectors, turbine blades, powders, films, foils, plates, molds (e.g.,wax molds, molds for injection-molding processes, investment-castingprocesses, etc.), fabrics (woven, felted, etc.), surgical instruments,medical implants, consumer packaged goods, shoes, bicycles, automobiles,automotive or aerospace parts (e.g., frames, body panels, etc.),appliances (e.g., microwaves, ovens, refrigerators, etc.), devicehousings (e.g., for watches, computers, smartphones, tablet computers,wearable electronic devices, or the like or any combination thereof).

Accordingly, materials that may be processed include one or more metalssuch as Al, Ag, Au, Cu, Fe, In, Mg, Pt, Sn, Ti, or the like, or anycombination thereof (e.g., whether as an alloy, composite, etc.),conductive metal oxides (e.g., ITO, etc.), transparent conductivepolymers, ceramics, waxes, resins, inorganic dielectric materials (e.g.,used as interlayer dielectric structures, such as silicon oxide, siliconnitride, silicon oxynitride, or the like or any combination thereof),low-k dielectric materials (e.g., methyl silsesquioxane (MSQ), hydrogensilsesquioxane (HSQ), fluorinated tetraethyl orthosilicate (FTEOS), orthe like or any combination thereof), organic dielectric materials(e.g., SILK, benzocyclobutene, Nautilus, (all manufactured by Dow),polyfluorotetraethylene, (manufactured by DuPont), FLARE, (manufacturedby Allied Chemical), or the like or any combination thereof), glassfibers, polymeric materials (polyamides, polyimides, polyesters,polyacetals, polycarbonates, modified polyphenylene ethers, polybutyleneterephthalates, polyphenylene sulfides, polyether sulfones, polyetherimides, polyether ether ketones, liquid crystal polymers, acrylonitrilebutadiene styrene, and any compound, composite, or alloy thereof),leather, paper, build-up materials (e.g., ANJINOMOTO Build-up Film, alsoknown as “ABF”, etc.), glass-reinforced epoxy laminate (e.g., FR4),prepregs, solder resist, or the like or any composite, laminate, orother combination thereof.

II. System—Overview

FIG. 1 schematically illustrates an apparatus for processing aworkpiece, in accordance with one embodiment of the present invention.

Referring to the embodiment shown in FIG. 1, an apparatus 100 forprocessing a workpiece includes a laser source 104 for generating laserpulses, a first positioner 106, a second positioner 108, a thirdpositioner 110, a scan lens 112 and a controller 114. In view of thedescription that follows, it should be recognized that inclusion of thefirst positioner 106 is optional (i.e., the apparatus 100 need notinclude the first positioner 106), provided that the apparatus 100includes the second positioner 108 or the third positioner 110.Likewise, it should be recognized that inclusion of the secondpositioner 108 is optional (i.e., the apparatus 100 need not include thesecond positioner 108), provided that the apparatus 100 includes thefirst positioner 106 or the third positioner 110. Lastly, it shouldsimilarly be recognized that inclusion of the third positioner 110 isoptional (i.e., the apparatus 100 need not include the third positioner110), provided that the apparatus 100 includes the first positioner 106or the second positioner 108.

Although not illustrated, the apparatus 100 also includes one or moreoptical components (e.g., beam expanders, beam shapers, apertures,filters, collimators, lenses, mirrors, polarizers, wave plates,diffractive optical elements, refractive optical elements, or the likeor any combination thereof) to focus, expand, collimate, shape,polarize, filter, split, combine, crop, or otherwise modify, condition,direct, monitor or measure laser pulses generated by the laser source104 along one or more beam paths (e.g., beam path 116) to the scan lens112. It will further be appreciated that one or more of theaforementioned components may be provided, or that the apparatus 100 mayfurther include one or more additional components, as disclosed in U.S.Pat. Nos. 4,912,487, 5,633,747, 5,638,267, 5,751,585, 5,847,960,5,917,300, 6,314,473, 6,430,465, 6,700,600, 6,706,998, 6,706,999,6,816,294, 6,947,454, 7,019,891, 7,027,199, 7,133,182, 7,133,186,7,133,187, 7,133,188, 7,245,412, 7,259,354, 7,611,745, 7,834,293,8,026,158, 8,076,605, 8,158,493, 8,288,679, 8,404,998, 8,497,450,8,648,277, 8,680,430, 8,847,113, 8,896,909, 8,928,853, 9,259,802 or inaforementioned U.S. Patent App. Pub. Nos. 2014/0026351, 2014/0197140,2014/0263201, 2014/0263212, 2014/0263223, 2014/0312013, or in GermanPatent No. DE102013201968B4, or in International Patent App. Pub. No.WO2009/087392, or any combination thereof, each of which is incorporatedherein by reference in its entirety.

Laser pulses transmitted through the scan lens 112 propagate along abeam axis so as to be delivered to the workpiece 102. Laser pulsesdelivered to the workpiece 102 may be characterized as having aGaussian-type spatial intensity profile or a non-Gaussian-type (i.e.,“shaped”) spatial intensity profile (e.g., a “top-hat” spatial intensityprofile). Regardless of the type of spatial intensity profile, thespatial intensity profile can also be characterized as a cross-sectionalshape of a laser pulse propagating along the beam axis (or beam path116), which may be circular, elliptical, rectangular, triangular,hexagonal, ring-shaped, etc., or arbitrarily shaped. Delivered laserpulses can be characterized as impinging the workpiece 102 at a spotsize in a range from 2 μm to 200 μm. As used herein, the term “spotsize” refers to the diameter or maximum spatial width of a deliveredlaser pulse at a location where the beam axis traverses a region of theworkpiece 102 (also referred to as a “process spot,” “spot location” or,more simply, a “spot”) that is to be, at least partially, processed bythe delivered laser pulse.

For purposes of discussion herein, spot size is measured as a radial ortransverse distance from the beam axis to where the optical intensitydrops to, at least, 1/e² of the optical intensity at the beam axis.Generally, the spot size of a laser pulse will be at a minimum at thebeam waist. It will be appreciated, however, that the spot size can bemade smaller than 2 μm or larger than 200 μm. Thus, at least one laserpulse delivered to the workpiece 102 can have a spot size greater thanor equal to 2 μm, 3 μm, 5 μm, 7 μm, 10 μm, 15 μm, 30 μm, 35 μm, 40 μm,45 μm, 50 μm, 55 μm, 80 μm, 100 μm, 150 μm, 200 μm, etc., or between anyof these values. Likewise, at least one delivered laser pulse can have aspot size less than 200 μm, 150 μm, 100 μm, 80 μm, 55 μm, 50 μm, 45 μm,40 μm, 35 μm, 30 μm, 15 μm, 10 μm, 7 μm, 5 μm, 3 μm, 2 μm, etc., orbetween any of these values. In one embodiment, laser pulses deliveredto the workpiece 102 can have a spot size in a range from 25 μm to 60μm. In another embodiment, laser pulses delivered to the workpiece 102can have a spot size in a range from 35 μm to 50 μm.

A. Laser Source

Generally, the laser source 104 is operative to generate laser pulses.As such, the laser source 104 may include a pulse laser source, a CWlaser source, a QCW laser source, a burst mode laser, or the like or anycombination thereof. In the event that the laser source 104 includes aQCW or CW laser source, the laser source 104 may further include a pulsegating unit (e.g., an acousto-optic (AO) modulator (AOM), a beamchopper, etc.) to temporally modulate beam of laser radiation outputfrom the QCW or CW laser source. Although not illustrated, the apparatus100 may optionally include one or more harmonic generation crystals(also known as “wavelength conversion crystals”) configured to convert awavelength of light output by the laser source 104. Accordingly, laserpulses ultimately delivered to the workpiece 102 may be characterized ashaving one or more wavelengths in one or more of the ultra-violet (UV),visible (e.g., violet, blue, green, red, etc.), or infrared (IR) (e.g.,near-IR (NIR) spanning a wavelength range from 750 nm to 1.4 μm,short-wavelength IR (SWIR) spanning a wavelength range from 1.4 μm to 3μm, mid-wavelength IR (MWIR) spanning a wavelength range of 3 μm to 8μm, or long-wavelength IR (LWIR) spanning a wavelength range of 8 μm to15 μm) ranges of the electromagnetic spectrum, or any combinationthereof.

In another embodiment, the laser source 104 may be provided as a QCW orCW laser source and not include a pulse gating unit. In such anembodiment, the laser source 104 may generate a continuous (non-pulsed)laser beam for subsequent propagation along the beam path 116. Thus, thelaser source 104 can be broadly characterized as operative to generate abeam of laser energy, which may manifested as a series of laser pulsesor as a continuous laser beam, which can thereafter be propagated alongthe beam path 116. Although many embodiments discussed herein makereference to laser pulses, it should be recognized that continuous beamsmay alternatively, or additionally, be employed whenever appropriate.

Laser pulses output by the laser source 104 can have a pulse width orpulse duration (i.e., based on the full-width at half-maximum (FWHM) ofthe optical power in the pulse versus time) that is in a range from 10fs to 900 ms. It will be appreciated, however, that the pulse durationcan be made smaller than 30 fs or larger than 900 ms. Thus, at least onelaser pulse output by the laser source 104 can have a pulse durationgreater than or equal to 10 fs, 15 fs, 30 fs, 50 fs, 100 fs, 150 fs, 200fs, 300 fs, 500 fs, 700 fs, 750 fs, 850 fs, 900 fs, 1 ps, 2 ps, 3 ps, 4ps, 5 ps, 7 ps, 10 ps, 15 ps, 25 ps, 50 ps, 75 ps, 100 ps, 200 ps, 500ps, 1 ns, 1.5 ns, 2 ns, 5 ns, 10 ns, 20 ns, 50 ns, 100 ns, 200 ns, 400ns, 800 ns, 1000 ns, 2 μs, 5 μs, 10μs, 50μs, 100 μs, 300 μs, 500 μs, 900μs, 1 ms, 2 ms, 5 ms, 10 ms, 20 ms, 50 ms, 100 ms, 300 ms, 500 ms, 900ms, 1 s, etc., or between any of these values. Likewise, at least onelaser pulse output by the laser source 104 can have a pulse durationless than 1 s, 900 ms, 500 ms, 300 ms, 100 ms, 50 ms, 20 ms, 10 ms, 5ms, 2 ms, 1 ms, 300 ms, 900 μs, 500 μs, 300 μs, 100 μs, 50 μs, 10 μs, 5μs, 1 μs, 800 ns, 400 ns, 200 ns, 100 ns, 50 ns, 20 ns, 10 ns, 5 ns, 2ns, 1.5 ns, 1 ns, 500 ps, 200 ps, 100 ps, 75 ps, 50 ps, 25 ps, 15 ps, 10ps, 7 ps, 5 ps, 4 ps, 3 ps, 2 ps, 1 ps, 900 fs, 850 fs, 750 fs, 700 fs,500 fs, 300 fs, 200 fs, 150 fs, 100 fs, 50 fs, 30 fs, 15 fs, 10 fs,etc., or between any of these values. In one embodiment, laser pulsesoutput by the laser source 104 have a pulse duration in a range from 3ps to 15 ps. In another embodiment, laser pulses output by the lasersource 104 have a pulse duration in a range from 5 ps to 7 ps.

Laser pulses output by the laser source 104 can have an average power ina range from 100 mW to 50 kW. It will be appreciated, however, that theaverage power can be made smaller than 100 mW or larger than 50 kW.Thus, laser pulses output by the laser source 104 can have an averagepower greater than or equal to 100 mW, 300 mW, 500 mW, 800 mW, 1 W, 2 W,3 W, 4 W, 5 W, 6 W, 7 W, 10 W, 15 W, 18 W, 25 W, 30 W, 50 W, 60 W, 100W, 150 W, 200 W, 250 W, 500 W, 2 kW, 3 kW, 20 kW, 50 kW, etc., orbetween any of these values. Likewise, laser pulses output by the lasersource 104 can have an average power less than 50 kW, 20 kW, 3 kW, 2 kW,500 W, 250 W, 200 W, 150 W, 100 W, 60 W, 50 W, 30 W, 25 W, 18 W, 15 W,10 W, 7 W, 6 W, 5 W, 4 W, 3 W, 2 W, 1 W, 800 mW, 500 mW, 300 mW, 100 mW,etc., or between any of these values.

Laser pulses can be output by the laser source 104 at a pulse repetitionrate in a range from 5 kHz to 1 GHz. It will be appreciated, however,that the pulse repetition rate can be less than 5 kHz or larger than 1GHz. Thus, laser pulses can be output by the laser source 104 at a pulserepetition rate greater than or equal to 5 kHz, 50 kHz, 100 kHz, 175kHz, 225 kHz, 250 kHz, 275 kHz, 500 kHz, 800 kHz, 900 kHz, 1 MHz, 1.5MHz, 1.8 MHz, 1.9 MHz, 2 MHz, 2.5 MHz, 3 MHz, 4 MHz, 5 MHz, 10 MHz, 20MHz, 50 MHz, 70 MHz, 100 MHz, 150 MHz, 200 MHz, 250 MHz, 300 MHz, 350MHz, 500 MHz, 550 MHz, 700 MHz, 900 MHz, 2 GHz, 10 GHz, etc., or betweenany of these values. Likewise, laser pulses can be output by the lasersource 104 at a pulse repetition rate less than 10 GHz, 2 GHz, 1 GHz,900 MHz, 700 MHz, 550 MHz, 500 MHz, 350 MHz, 300 MHz, 250 MHz, 200 MHz,150 MHz, 100 MHz, 90 MHz, 70 MHz, 50 MHz, 20 MHz, 10 MHz, 5 MHz, 4 MHz,3 MHz, 2.5 MHz, 2 MHz, 1.9 MHz, 1.8 MHz, 1.5 MHz, 1 MHz, 900 kHz, 800kHz, 500 kHz, 275 kHz, 250 kHz, 225 kHz, 175 kHz, 100 kHz, 50 kHz, 5kHz, etc., or between any of these values.

In addition to wavelength, pulse duration, average power and pulserepetition rate, laser pulses delivered to the workpiece 102 can becharacterized by one or more other characteristics such as pulse energy,peak power, etc., which can be selected (e.g., optionally based on oneor more other characteristics such as wavelength, pulse duration,average power and pulse repetition rate, etc.) to irradiate theworkpiece 102 at the process spot at an optical intensity (measured inW/cm²), fluence (measured in J/cm²), etc., sufficient to process theworkpiece 102 (e.g., to form one or more features having one or moredesired characteristics, to prevent the workpiece 102 from beingundesirably damaged during formation of the feature(s), or the like orany combination thereof).

Examples of types of lasers that the laser source 104 may becharacterized as gas lasers (e.g., carbon dioxide lasers, carbonmonoxide lasers, excimer lasers, etc.), solid-state lasers (e.g., Nd:YAGlasers, etc.), rod lasers, fiber lasers, photonic crystal rod/fiberlasers, passively mode-locked solid-state bulk or fiber lasers, dyelasers, mode-locked diode lasers, pulsed lasers (e.g., ms-, ns-, ps-,fs-pulsed lasers), CW lasers, QCW lasers, or the like or any combinationthereof. Depending upon their configuration, gas lasers (e.g., carbondioxide lasers, etc.) may be configured to operate in one or more modes(e.g., in CW mode, QCW mode, pulsed mode, or any combination thereof).Specific examples of laser sources that may be provided as the lasersource 104 include one or more laser sources such as: the BOREAS, HEGOA,SIROCCO or CHINOOK series of lasers manufactured by EOLITE; the PYROFLEXseries of lasers manufactured by PYROPHOTONICS; the PALADIN Advanced 355or DIAMOND series (e.g., DIAMOND E-, G-, J-2, J-3, J-5 series) of lasersmanufactured by COHERENT; the PULSTAR- or FIRESTAR-series lasersmanufactured by SYNRAD; the TRUFLOW-series of lasers (e.g., TRUFLOW2000, 2700, 3000, 3200, 3600, 4000, 5000, 6000, 7000, 8000, 10000,12000, 15000, 20000), TRUCOAX-series of lasers (e.g., TRUCOAX 1000) orthe TRUDISK-, TRUPULSE-, TRUDIODE-, TRUFIBER-, or TRUMICRO-series oflasers, all manufactured by TRUMPF; the FCPA μJEWEL or FEMTOLITE seriesof lasers manufactured by IMRA AMERICA; the TANGERINE and SATSUMA serieslasers (and MIKAN and T-PULSE series oscillators) manufactured byAMPLITUDE SYSTEMES; CL-, CLPF-, CLPN-, CLPNT-, CLT-, ELM-, ELPF-, ELPN-,ELPP-, ELR-, ELS-, FLPN-, FLPNT-, FLT-, GLPF-, GLPN-, GLR-, HLPN-,HLPP-, RFL-, TLM-, TLPN-, TLR-, ULPN-, ULR-, VLM-, VLPN-, YLM-, YLPF-,YLPN-, YLPP-, YLR-, YLS-, FLPM-, FLPMT-, DLM-, BLM-, or DLR-series oflasers manufactured by IPG PHOTONICS (e.g., including the GPLN-100-M,GPLN-500-QCW, GPLN-500-M, GPLN-500-R, GPLN-2000-S, etc.), or the like orany combination thereof.

B. First Positioner

The first positioner 106 is arranged, located or otherwise disposed inthe beam path 116 and is operative to diffract, reflect, refract, or thelike, or any combination thereof, laser pulses that are generated by thelaser source 104 (i.e., to “deflect” the laser pulses) so as to impartmovement of the beam path 116 (e.g., relative to the scan lens 112) and,consequently, impart movement of the beam axis relative to the workpiece102. Generally, the first positioner 106 is configured to impartmovement of the beam axis relative to the workpiece 102 along X- andY-axes (or directions). Although not illustrated, the X-axis (orX-direction) will be understood to refer to an axis (or direction) thatis orthogonal to the illustrated Y- and Z-axes (or directions).

Movement of the beam axis relative to the workpiece 102, as imparted bythe first positioner 106, is generally limited such that the processspot can be scanned, moved or otherwise positioned within a first scanfield or “first scanning range” that extends between 0.01 mm to 4.0 mmin the X- and Y-directions. It will be appreciated, however, that thefirst scanning range may extend less than 0.01 mm or more than 4.0 mm inany of the X- or Y-directions (e.g., depending upon one or more factorssuch as the configuration of the first positioner 106, the location ofthe first positioner 106 along the beam path 116, the beam size of thelaser pulses incident upon the first positioner 106, the spot size,etc.). Thus, the first scanning range may extend, in any of the X- andY-directions a distance that is greater than or equal to 0.04 mm, 0.1mm, 0.5 mm, 1.0 mm, 1.4 mm, 1.5 mm, 1.8 mm, 2 mm, 2.5 mm, 3.0 mm, 3.5mm, 4.0 mm, 4.2 mm, etc., or between any of these values. Likewise, thefirst scanning range may extend, in any of the X- and Y-directions adistance that is less than to 5 mm, 4.2 mm, 4.0 mm, 3.5 mm, 3.0 mm, 2.5mm, 2.0 mm, 1.8 mm, 1.5 mm, 1.4 mm, 1.0 mm, 0.5 mm, 0.1 mm, 0.04 mm,0.01 mm, etc., or between any of these values. As used herein, the term“beam size” refers to the diameter or width of a laser pulse, and can bemeasured as a radial or transverse distance from the beam axis to wherethe optical intensity drops to 1/e² of the optical intensity at the axisof propagation along the beam path 116. Thus in some embodiments, amaximum dimension of the first scanning range (e.g., in the X- orY-directions, or otherwise) may be greater than or equal to acorresponding maximum dimension (as measured in the X-Y plane) of afeature (e.g., an opening, a recess, a via, a trench, etc.) to be formedin the workpiece 102. In another embodiment however, the maximumdimension of the first scanning range may be less than the maximumdimension of the feature to be formed.

Generally, the rate (also referred to as a “positioning rate”) withwhich the first positioner 106 is capable of positioning the processspot at any location within the first scanning range (thus moving thebeam axis) is in a range from 50 kHz (or thereabout) to 10 MHz (orthereabout). This range is also referred to herein as the firstpositioning bandwidth. The inverse of the positioning rate is hereinreferred to as the “positioning period,” and refers to the minimumamount of time necessary to change the position the process spot fromone location within the first scanning range to any other locationwithin the first scanning range. Thus, the first positioner 106 can becharacterized by a positioning period in a range from 20 μs (orthereabout) to 0.1 μs (or thereabout). In one embodiment, the firstpositioning bandwidth is in a range from 100 kHz (or thereabout) to 2MHz (or thereabout). For example, the first positioning bandwidth of 1MHz (or thereabout).

The first positioner 106 can be provided as amicro-electro-mechanical-system (MEMS) mirror or mirror array, an AOdeflector (AOD) system, an electro-optic deflector (EOD) system, afast-steering mirror (FSM) element incorporating a piezoelectricactuator, electrostrictive actuator, voice-coil actuator, etc., or thelike or any combination thereof. In one embodiment, the first positioner106 is provided as an AOD system including at least one (e.g., one, two,etc.) single-element AOD system, at least one (e.g., one, two, etc.)phased-array AOD system, or the like or any combination thereof. BothAOD systems include an AO cell formed of a material such as crystallineGe, PbMoO₄, or TeO₂, glassy SiO₂, quartz, As₂S₃, etc. As used herein, a“single-element” AOD system refers to an AOD system having only a singleultrasonic transducer element acoustically coupled to the AO cell,whereas a “phased-array” AOD system includes a phased-array of at leasttwo ultrasonic transducer elements acoustically coupled to a common AOcell.

As will be recognized by those of ordinary skill, acousto-optic (AO)technology (e.g., AODs, AOMs, etc.) utilize diffraction effects causedby acoustic waves propagating through the AO cell to modulate one ormore characteristics of an optical wave (i.e., a beam of laser energy,in the context of the present application) contemporaneously propagatingthrough the AO cell. Typically the AO cell is capable of supporting boththe acoustic wave and the optical wave in the same region. The acousticwave imparts a perturbation to the index of refraction in the AO cell.Acoustic waves are typically launched into the AO cell by driving theultrasonic transducer element at one or more RF frequencies. Bycontrolling characteristics of the acoustic wave (e.g., amplitude,frequency, phase, etc.) one or more characteristics of the propagatingoptic wave may be controllably modulated to impart movement of the beampath 116 (e.g., relative to the scan lens 112). It should also berecognized that characteristics of an acoustic wave launched into an AOcell can be controlled using well-known techniques to attenuate theenergy in a beam of laser energy as it transits the AO cell.Accordingly, an AOD system can also be operated to modulate the pulseenergy (and, correspondingly, the fluence, peak power, opticalintensity, average power, etc.) of laser pulses ultimately delivered tothe workpiece 102.

It will be appreciated that the material from which the AO cell isformed will depend upon the wavelength of the laser pulses thatpropagate along the beam path 116 so as to be incident upon the AO cell.For example, a material such as crystalline Ge can be used where thewavelength of laser pulses to be deflected is in a range from 2 μm (orthereabout) to 12 μm (or thereabout), materials such as quartz and TeO₂can be used where the wavelength of laser pulses to be deflected is in arange from 200 nm (or thereabout) to 5 μm (or thereabout).

It should be recognized that AOD systems are dispersive elements and,consequently, desirably deflect laser pulses having suitably narrowspectral linewidth (e.g., based on the full-width at half-maximum (FWHM)of the optical power spectral density in the pulse). A laser source 104configured to generate laser pulses having one or more wavelengths inone or more of the ultra-violet, visible, or NIR range will typicallyproduce laser pulses having a suitably narrow spectral linewidth. Lasersources 104 such as high power CW gas lasers (e.g., carbon dioxide orcarbon monoxide CW lasers with an average power greater than about 300W) and other low power CW or pulsed gas lasers (e.g., with an averagepower less than about 300 W) can similarly generate laser pulses havinga suitably narrow spectral linewidth in the SWIR, MWIR or LWIR range.Conventionally, high power pulsed gas lasers (e.g., carbon dioxide orcarbon monoxide pulsed lasers with an average power greater than about300 W) capable of generating laser pulses are based on a MasterOscillator Power Amplifier (MOPA) laser system architecture.

Any of the AOD systems may be provided as single-axis AOD system (e.g.,configured impart movement of the beam axis along a single direction) oras a multi-axis AOD system (e.g., configured impart movement of the beamaxis along a multiple directions, e.g., X- and Y-directions) bydeflecting the beam path 116. Generally, a multi-axis AOD system can beprovided as a multi-cell system or a single-cell system. A multi-cell,multi-axis system typically includes multiple AOD systems, eachconfigured to impart movement of the beam axis along a different axis.For example, a multi-cell, multi-axis system can include a first AODsystem (e.g., a single-element or phased-array AOD system) configured toimpart movement of the beam axis along the X-direction (e.g., an “X-axisAOD system”), and a second AOD system (e.g., a single-element orphased-array AOD system) configured to impart movement of the beam axisalong the Y-direction (e.g., a “Y-axis AOD system”). A single-cell,multi-axis system (e.g., an “X/Y-axis AOD system”) typically includes asingle AOD system configured to impart movement of the beam axis alongthe X- and Y-directions. For example, a single-cell system can includeat least two ultrasonic transducer elements acoustically coupled todifferent planes, facets, sides, etc., of a common AO cell.

C. Second Positioner

Like the first positioner 106, the second positioner 108 is disposed inthe beam path 116 and is operative to diffract, reflect, refract, or thelike or any combination thereof, laser pulses that are generated by thelaser source 104 and passed by the first positioner 106 so as to impartmovement of the beam axis (e.g., along X- and Y-directions) relative tothe workpiece 102, via movement of the beam path 116 relative to thescan lens 112. Movement of the beam axis relative to the workpiece 102,as imparted by the second positioner 108, is generally limited such thatthe process spot can be scanned, moved or otherwise positioned within asecond scan field or “scanning range” that extends in the X- and/orY-directions over an area that is greater than the first scanning range.In view of the configuration described herein, it should be recognizedthat movement of the beam axis imparted by the first positioner 106 canbe superimposed by movement of the beam axis imparted by the secondpositioner 108. Thus, the second positioner 108 is operative to scan thefirst scanning range within the second scanning range.

In one embodiment, the second scanning range extends between 1 mm to 50mm in the X- and/or Y-directions. In another embodiment, the secondscanning range extends between 15 mm to 30 mm in the X- and/orY-directions. It will be appreciated, however, that the secondpositioner 108 may be configured such that the second scanning rangeextends less than 1 mm or more than 50 mm in any of the X- orY-directions. Thus in some embodiments, a maximum dimension of thesecond scanning range (e.g., in the X- or Y-directions, or otherwise)may be greater than or equal to a corresponding maximum dimension (asmeasured in the X-Y plane) of a feature (e.g., a via, a trench, a scribeline, a recessed region, a conductive trace, etc.) to be formed in theworkpiece 102. In another embodiment however, the maximum dimension ofthe second scanning range may be less than the maximum dimension of thefeature to be formed.

Generally, the positioning rate with which the second positioner 108 iscapable of positioning the process spot at any location within thesecond scanning range (thus moving the beam axis within the secondscanning range and/or scanning the first scanning range within thesecond scanning range) spans a range (also referred to herein as the“second positioning bandwidth”) that is less than the first positioningbandwidth. In one embodiment, the second positioning bandwidth is in arange from 900 Hz to 5 kHz. In another embodiment, the first positioningbandwidth is in a range from 2 kHz to 3 kHz (e.g., about 2.5 kHz).

The second positioner 108 can be provided as a galvanometer mirrorsystem including two galvanometer mirror components, where onegalvanometer mirror component is arranged to impart movement of the beamaxis relative to the workpiece 102 along the X-direction and anothergalvanometer mirror component is arranged to impart movement of the beamaxis relative to the workpiece 102 along the Y-direction. In otherembodiments, however, the second positioner 108 may be provided as arotating polygon mirror system, etc. It will thus be appreciated that,depending on the specific configuration of the second positioner 108 andthe first positioner 106, the second positioning bandwidth may begreater than or equal to the first positioning bandwidth.

D. Third Positioner

The third positioner 110 is operative to impart movement of theworkpiece 102 relative to the scan lens 112, and, consequently, movementof the workpiece 102 relative to the beam axis. Movement of theworkpiece 102 relative to the beam axis is generally limited such thatthe process spot can be scanned, moved or otherwise positioned within athird scan field or “scanning range” that extends in the X- and/orY-directions over an area that is greater than the second scanningrange. In one embodiment, the third scanning range extends between 25 mmto 2 m in the X- and/or Y-directions. In another embodiment, the thirdscanning range extends between 0.5 m to 1.5 m in the X- and/orY-directions. Generally, a maximum dimension of the third scanning range(e.g., in the X- or Y-directions, or otherwise) will be greater than orequal to a corresponding maximum dimension (as measured in the X-Yplane) of any feature to be formed in the workpiece 102. Optionally, thethird positioner 110 may be configured to move the workpiece 102relative to the beam axis within a scanning range that extends in theZ-direction (e.g., over a range between 1 mm and 50 mm). Thus, the thirdscanning range may extend along the X-, Y- and/or Z-directions.

In view of the configuration described herein, it should be recognizedthat movement of the beam axis imparted by the first positioner 106and/or the second positioner 108 can be superimposed by movement of theworkpiece 102 imparted by the third positioner 110. Thus, the thirdpositioner 110 is operative to scan the first scanning range and/orsecond scanning range within the third scanning range. Generally, thepositioning rate with which the third positioner 110 is capable ofpositioning the process spot at any location within the third scanningrange (thus moving the workpiece 102, scanning the first scanning rangewithin the third scanning range, and/or scanning the second scanningrange within the third scanning range) spans a range (also referred toherein as the “third positioning bandwidth”) that is less than thesecond positioning bandwidth. In one embodiment, the third positioningbandwidth is in a range of 10 Hz (or thereabout), or less.

In one embodiment, the third positioner 110 is provided as one or morelinear stages (e.g., each capable of imparting translational movement tothe workpiece 102 along the X-, Y- and/or Z-directions), one or morerotational stages (e.g., each capable of imparting rotational movementto the workpiece 102 about an axis parallel to the X-, Y- and/orZ-directions), or the like or any combination thereof. In oneembodiment, the third positioner 110 includes an X-stage for moving theworkpiece 102 along the X-direction, and a Y-stage supported by theX-stage (and, thus, moveable along the X-direction by the X-stage) formoving the workpiece 102 along the Y-direction. Although not shown, theapparatus 100 may also include an optional base (e.g., a granite block)that supports the third positioner 110.

Although not shown, the apparatus 100 may include an optional chuckcoupled to the third positioner 110, to which the workpiece 102 can bemechanically clamped, fixed, held, secured or be otherwise supported. Inone embodiment, the workpiece 102 can be clamped, fixed, held, securedor be otherwise supported so as to directly contact a main, typicallyflat, support surface of the chuck. In another embodiment, the workpiece102 can be clamped, fixed, held, secured or be otherwise supported so asto be spaced apart from the support surface of the chuck. In anotherembodiment, the workpiece 102 can be fixed, held, or secured by way of aforce (e.g., an electrostatic force, a vacuum force, a magnetic force)applied to the workpiece 102 from the chuck, or otherwise presentbetween the workpiece 102 and the chuck.

As described thus far, the apparatus 100 employs a so-called “stacked”positioning system, in which positions of the components such as thefirst positioner 106, second positioner 108, scan lens 112, etc., arekept stationary within the apparatus 100 (e.g., via one or moresupports, frames, etc., as is known in the art) relative to theworkpiece 102, which is moved via the third positioner 110. In anotherembodiment, the third positioner 110 may be arranged and configured tomove one or more components such as the first positioner 106, secondpositioner 108, scan lens 112, etc., and the workpiece 102 may be keptstationary. In yet another embodiment, the apparatus 100 can employ asplit-axis positioning system in which one or more components such asthe first positioner 106, second positioner 108, scan lens 112, etc.,are carried by one or more linear or rotational stages. In such anembodiment, the third positioner 110 includes one or more linear orrotational stages arranged and configured to move one or more componentssuch as the first positioner 106, second positioner 108, scan lens 112,etc., and one or more linear or rotational stages arranged andconfigured to move the workpiece 102. Thus, the third positioner 110imparts movement of the workpiece 102, of the scan lens 112 (or scanhead associated with the scan lens 112, as discussed below). Someexamples of split-axis positioning systems that may be beneficially oradvantageously employed in the apparatus 100 include any of thosedisclosed in U.S. Pat. Nos. 5,751,585, 5,798,927, 5,847,960, 6,706,999,7,605,343, 8,680,430, 8,847,113, or in U.S. Patent App. Pub. No.2014/0083983, or any combination thereof, each of which is incorporatedherein by reference in its entirety.

In another embodiment, one or more components such as the firstpositioner 106, second positioner 108, scan lens 112, etc., may becarried by an articulated, multi-axis robotic arm (e.g., a 2-, 3-, 4-,5-, or 6-axis arm). In such an embodiment, the second positioner 108and/or scan lens 112 may, optionally, be carried by an end effector ofthe robotic arm. In yet another embodiment, the workpiece 102 may becarried directly on an end effector of an articulated, multi-axisrobotic arm (i.e., without the third positioner 110). In still anotherembodiment, the third positioner 110 may be carried on an end effectorof an articulated, multi-axis robotic arm.

D. Scan Lens

The scan lens 112 (e.g., provided as either a simple lens, or a compoundlens) is generally configured to focus laser pulses directed along thebeam path, typically so as to produce a beam waist that can bepositioned at the desired process spot. The scan lens 112 may beprovided as an f-theta lens, a telecentric lens, an axicon lens (inwhich case, a series of beam waists are produced, yielding a pluralityof process spots displaced from one another along the beam axis), or thelike or any combination thereof. In one embodiment, the scan lens 112 isprovided as a fixed-focal length lens and is coupled to a lens actuator(not shown) configured to move the scan lens 112 (e.g., so as to changethe position of the beam waist along the beam axis). For example, thelens actuator may be provided as a voice coil configured to linearlytranslate the scan lens 112 along the Z-direction. In anotherembodiment, the scan lens 112 is provided as a variable-focal lengthlens (e.g., a zoom lens, or a so-called “liquid lens” incorporatingtechnologies currently offered by COGNEX, VARIOPTIC, etc.) capable ofbeing actuated (e.g., via a lens actuator) to change the position of thebeam waist along the beam axis.

In one embodiment, the scan lens 112 and the second positioner 108 areintegrated into a common housing or “scan head” 118. Thus, in anembodiment in which the apparatus 100 includes a lens actuator, the lensactuator may be coupled to the scan lens 112 (e.g., so as to enablemovement of the scan lens 112 within the scan head 118, relative to thesecond positioner 108). Alternatively, the lens actuator may be coupledto the scan head 118 (e.g., so as to enable movement of the scan head118 itself, in which case the scan lens 112 and the second positioner108 would move together). In another embodiment, the scan lens 112 andthe second positioner 108 are integrated into different housings (e.g.,such that the housing in which the scan lens 112 is integrated ismovable relative to the housing in which the second positioner 108 isintegrated). Components of the scan head 118, or the entire scan head118 itself, may be of a modular assembly, such that a component of thescan head 118 can be simply removed and replaced with another component,such that one scan head 118 can be simply removed and replaced withanother scan head, etc.

E. Controller

Generally, the controller 114 is communicatively coupled (e.g., over oneor more wired or wireless communications links, such as USB, Ethernet,Firewire, Wi-Fi, RFID, NFC, Bluetooth, Li-Fi, or the like or anycombination thereof) to one or more components of the apparatus 100,such as the laser source 104, the first positioner 106, the secondpositioner 108, third positioner 110, the lens actuator, etc., and arethus operative in response to one or more control signals output by thecontroller 114.

For example, the controller 114 may control an operation of the firstpositioner 106, second positioner 108, or third positioner 110, toimpart relative movement between the beam axis and the workpiece so asto cause relative movement between the process spot and the workpiece102 along a path or trajectory (also referred to herein as a “processtrajectory”) within the workpiece 102. It will be appreciated that anytwo of these positioners, or all three of these positioners, may becontrolled such that two positioners (e.g., the first positioner 106 andthe second positioner 108, the first positioner 106 and the thirdpositioner 110, or the second positioner 108 and the third positioner110), or all three positioners simultaneously impart relative movementbetween the process spot and the workpiece 102 (thereby imparting a“compound relative movement” between the beam axis and the workpiece).Of course, at any time, it is possible to control only one positioner(e.g., the first positioner 106, the second positioner 108 or the thirdpositioner 110) to impart relative movement between the process spot andthe workpiece 102 (thereby imparting a “non-compound relative movement”between the beam axis and the workpiece).

Control signals to command compound or non-compound relative movementmay be pre-computed, or otherwise determined in real-time. In anotherexample, the controller 114 may control an operation of the firstpositioner 106 to change the spot shape or spot size of laser pulsesdelivered to the process spot (e.g., by chirping an RF signal applied toone or more ultrasonic transducer elements of one or more AOD systems inthe first positioner 106, by applying a spectrally-shaped RF signal toone or more ultrasonic transducer elements of one or more AOD systems inthe first positioner 106, or the like or any combination thereof).

Some examples of operations that one or more of the aforementionedcomponents can be controlled to perform include any operations,functions, processes, and methods, etc., as disclosed in aforementionedU.S. Pat. Nos. 4,912,487, 5,633,747, 5,638,267, 5,751,585, 5,847,960,5,917,300, 6,314,473, 6,430,465, 6,700,600, 6,706,998, 6,706,999,6,816,294, 6,947,454, 7,019,891, 7,027,199, 7,133,182, 7,133,186,7,133,187, 7,133,188, 7,245,412, 7,259,354, 7,611,745, 7,834,293,8,026,158, 8,076,605, 8,288,679, 8,404,998, 8,497,450, 8,648,277,8,680,430, 8,847,113, 8,896,909, 8,928,853, 9,259,802, or inaforementioned U.S. Patent App. Pub. Nos. 2014/0026351, 2014/0197140,2014/0263201, 2014/0263212, 2014/0263223, 2014/0312013, or in GermanPatent No. DE102013201968B4, or in International Patent App. No.WO2009/087392, or any combination thereof.

Generally, the controller 114 includes one or more processors configuredto generate the aforementioned control signals upon executinginstructions. A processor can be provided as a programmable processor(e.g., including one or more general purpose computer processors,microprocessors, digital signal processors, or the like or anycombination thereof) configured to execute the instructions.Instructions executable by the processor(s) may be implemented software,firmware, etc., or in any suitable form of circuitry includingprogrammable logic devices (PLDs), field-programmable gate arrays(FPGAs), field-programmable object arrays (FPGAs), application-specificintegrated circuits (ASICs)—including digital, analog and mixedanalog/digital circuitry—or the like, or any combination thereof.Execution of instructions can be performed on one processor, distributedamong processors, made parallel across processors within a device oracross a network of devices, or the like or any combination thereof.

In one embodiment, the controller 114 includes tangible media such ascomputer memory, which is accessible (e.g., via one or more wired orwireless communications links) by the processor. As used herein,“computer memory” includes magnetic media (e.g., magnetic tape, harddisk drive, etc.), optical discs, volatile or non-volatile semiconductormemory (e.g., RAM, ROM, NAND-type flash memory, NOR-type flash memory,SONOS memory, etc.), etc., and may be accessed locally, remotely (e.g.,across a network), or a combination thereof. Generally, the instructionsmay be stored as computer software (e.g., executable code, files,instructions, etc., library files, etc.), which can be readily authoredby artisans, from the descriptions provided herein, e.g., written in C,C++, Visual Basic, Java, Python, Tel, Perl, Scheme, Ruby, etc. Computersoftware is commonly stored in one or more data structures conveyed bycomputer memory.

Although not shown, one or more drivers (e.g., RF drivers, servodrivers, line drivers, power sources, etc.) can be communicativelycoupled to an input of one or more components such as the laser source104, the first positioner 106, the second positioner 108, the thirdpositioner 110, the lens actuator, a mechanism for effecting Z-heightcompensation (see below), etc. In one embodiment, each driver typicallyincludes an input to which the controller 114 is communicatively coupledand the controller 114 is thus operative to generate one or more controlsignals (e.g., trigger signals, etc.), which can be transmitted to theinput(s) of one or more drivers associated with one or more componentsof the apparatus 100. Thus, components such as the laser source 104, thefirst positioner 106, the second positioner 108, third positioner 110,the lens actuator, etc., are responsive to control signals generated bythe controller 114.

In another embodiment, and although not shown, one or more additionalcontrollers (e.g., component-specific controllers) may, optionally, becommunicatively coupled to an input of a driver communicatively coupledto a components (and thus associated with the component) such as thelaser source 104, the first positioner 106, the second positioner 108,the third positioner 110, the lens actuator, the mechanism for effectingZ-height compensation, etc. In this embodiment, each component-specificcontroller can be communicatively coupled and the controller 114 and beoperative to generate, in response to one or more control signalsreceived from the controller 114, one or more control signals (e.g.,trigger signals, etc.), which can then be transmitted to the input(s) ofthe driver(s) to which it is communicatively coupled. In thisembodiment, a component-specific controller may be configured assimilarly described with respect to the controller 114.

In another embodiment in which one or more component-specificcontrollers are provided, the component-specific controller associatedwith one component (e.g., the laser source 104) can be communicativelycoupled to the component-specific controller associated with onecomponent (e.g., the first positioner 106, etc.). In this embodiment,one or more of the component-specific controllers can be operative togenerate one or more control signals (e.g., trigger signals, etc.) inresponse to one or more control signals received from one or more othercomponent-specific controllers.

III. Embodiments Concerning the Second Positioner

Although particular embodiments in this section concerning the secondpositioner 108 are discussed in connection with the apparatus 100, itwill be appreciated that any one of these embodiments, or anycombination thereof, may be implemented in connection with anylaser-processing apparatus other than the apparatus 100. In someembodiments, the second positioner 108 is provided as a galvanometermirror system including a plurality of galvanometer mirror components(e.g., each including a mirror) disposed in the beam path.

For example, and with reference to FIG. 2, the galvanometer mirrorsystem is provided as galvanometer mirror system 200, which includes afirst galvanometer mirror component 202 a and a second galvanometermirror component 202 b. The first galvanometer mirror component 202 aincludes a first mirror 204 a coupled to a first mount 206 a, a firstmotor 208 a for rotating the first mirror 204 a via the first mount 206a and, optionally, a position detector (not shown) configured togenerate a position signal corresponding to the rotation of the firstmount 206 a about a first rotational axis 210 a, e.g., to enableclosed-loop servo control of the first motor 208 a. Similarly, thesecond galvanometer mirror component 202 b includes a second mirror 204b, a second mount 206 b and a second motor 208 b, each of which isconfigured as described above with respect to the first galvanometermirror component 202 a. The second galvanometer mirror component 202 bcan, optionally, include a position detector (not shown) configured togenerate a position signal corresponding to the rotation of the secondmount 206 b about a second rotational axis 210 b, e.g., to enableclosed-loop servo control of the second motor 208 b.

As exemplarily illustrated, the first mirror 204 a is disposed at afirst location in the beam path 116 (e.g., located relatively from thescan lens 112) and the second mirror 204 b is disposed at a secondlocation in the beam path 116 (e.g., located relatively close to thescan lens 112). The first mirror 204 a is rotatable about the firstrotational axis 210 a (e.g., the Y-axis) to reflect laser pulses andimpart movement of the beam path 116 (thereby imparting movement of thebeam axis within the second scanning range extending, for example, by adistance d(x) along the X-direction. Similarly, the second mirror 204 bis rotatable about the second rotational axis 210 b (e.g., the X-axis)to reflect laser pulses and impart movement of the beam path 116(thereby imparting movement of the beam axis within the second scanningrange extending, for example, by a distance d(y) along the Y-direction.In some embodiments, distances d(x) and d(y) can, as described above, bein a range from 1 mm to 200 mm. It will be appreciated, however, thatthe distances d(x) and d(y) can be in a range that is less than 1 mm orgreater than 200 mm. Thus, the distances d(x) and d(y) can be greaterthan or equal to 1 mm, 2 mm, 5 mm, 10 mm, 25 mm, 50 mm, 100 mm, 150 mm,160 mm, 170 mm, 200 mm, etc. Likewise, the distances d(x) and d(y) canbe less than greater than 200 mm, 170 mm, 160 mm, 150 mm, 100 mm, 50 mm,25 mm, 10 mm, 5 mm, 2 mm, 1 mm, etc., or between any of these values.

A. Telecentric Error

In one embodiment, the galvanometer mirror system 200 is configured suchthat the beam path, as deflected first by the first mirror 204 a andnext by the second mirror 204 b, intersects the pupil of the scan lens112 (or intersects at location of the scan lens 112 within a vicinity ofthe pupil) as the beam axis is moved within the second scanning range.However, it has been discovered that some configurations of thegalvanometer mirror system 200 cause the beam path, as deflected firstby the first mirror 204 a and next by the second mirror 204 b, tointersect the scan lens 112 at a location that is offset from the pupilthereof (or intersects a location of the scan lens 112 outside theaforementioned vicinity of the pupil), thus creating telecentric errorswhich result in laser pulses being delivered to locations that arepositionally offset from locations of desired process spots. Forexample, the inventors have discovered that a positional offset of ±0.8μm (in the X- and Y directions) can be noticed for each 1° angle ofdeflection at the first mirror 204 a, depending upon the worksurfaceZ-height. Much less positional offset was noticed for each angle ofdeflection at the second mirror 204 b. While not wishing to be bound byany particular theory, it is believed that the distance from the firstmirror 204 a to the scan lens 112 (which is greater than the distancebetween the second mirror 204 b and the scan lens 112) primarilycontributes to the creation of the observed telecentric errors andpositional offsets. These positional offsets can ultimately degrade thepositional accuracy and precision with features such as vias aredrilled.

To help maintain the positional accuracy and precision with whichfeatures such as vias are drilled, the first galvanometer mirrorcomponent 202 a can be driven (e.g., in response to one or more controlsignals output by the controller 114, in response to electric currentoutput by a servo driver connected to the first galvanometer mirrorcomponent 202 a, etc.) to rotate the first mirror 204 a about the firstrotational axis 210 a to impart movement of the beam path 116 so as toimpart movement of the beam axis within the second scanning rangeextending, for example, by a distance d′(x), less than d(x), along theX-direction. Upon limiting the extent of the second scanning range inthe X-direction, the extent of the second scanning range in theY-direction can be increased to a distance d′(y), which can greater thanthe distance d(y) as exemplarily described above. See, e.g., FIG. 3,which illustrates second scanning ranges in accordance with twoembodiments of the present invention. Second scanning range 302 arepresents a typical scanning range where distances d(x) and d(y) areequal to each other. Second scanning range 302 b represents anotherscanning range where distances d′(x) and d′(y) are not equal to oneanother (i.e., distance d′(x) is less than distance d′(y)). In processessuch as via drilling processes, distance d′(x) may be in a range from0.04 mm to 200 mm. It will be appreciated, however, that distance d′(x)may be less than 0.04 mm or greater than 200 mm. For example, distanced′(x) may be greater than 0.04 mm, 0.1 mm, 0.5 mm, 1 mm, 2 mm, 5 mm, 10mm, 15 mm, 20 mm, 25 mm, 40 mm, 70 mm, 100 mm, 150 mm, etc., or betweenany of these values, while still being less than distance d′(y)Likewise, distance d′(x) may be less than 30 mm, 25 mm, 20 mm, 15 mm, 10mm, 5 mm, 2 mm, 1 mm, 0.5 mm, etc., or between any of these values.

To the extent that any undesirable positional offset attributable totelecentric errors created upon rotating the second mirror 204 b aredetected, the second galvanometer mirror component 202 b can besimilarly driven to rotate the second mirror 204 b about the secondrotational axis 210 b to impart movement of the beam path 116 so as toimpart movement of the beam axis within the second scanning rangeextending, for example, by a modified distance that is less than d(y)along the Y-direction (where such modified distance is larger thandistance d′(x)).

Notwithstanding the above, it will be appreciated that telecentric errorcan be reduced or eliminated by replacing the galvanometer mirror system200 with a positioner such as a two-axis FSM element (e.g., capable ofdeflecting the beam path along the X- and Y-directions) incorporating apiezoelectric actuator, electrostrictive actuator, voice-coil actuator,etc., or the like or any combination thereof.

IV. Embodiments Concerning Z-Height Measurement and Compensation

Often, the length of the portion of the beam path extending from theoutput of the apparatus 100 (e.g., the scan lens 112, in the illustratedembodiment) to the desired process spot location (i.e., the distancethat a laser pulse travels upon exiting the apparatus 100 until it isdelivered to the workpiece at the process spot) is referred to as the“Z-height.” For many laser-based processes, laser pulses typically yieldthe best process spot quality (e.g., in terms of size, shape, anduniformity) and highest fluence at the beam waist (i.e., when the spotsize of the delivered laser pulse at the process spot is equal (or atleast substantially equal) to the spot size at the beam waist). Otherlaser-based processes, however, do not require the spot size of adelivered laser pulse at the process spot to be equal (or evensubstantially equal) to the spot size at the beam waist. Nevertheless,deviations in the spot size of a delivered laser pulse at a desiredprocess spot away from a desired spot size can result in undesirably lowfluence levels, and change the dimension and intensity distribution ofthe delivered laser pulse at the desired process spot. These deviationscan affect the quality and/or throughput of the laser process.

To ensure that a laser pulse delivered to a desired process spot has adesired spot size, the apparatus 100 can optionally be provided with aZ-height sensor 124 configured to measure a distance between (or acharacteristic indicative of the distance between) the scan lens 112 anda region of the worksurface 102 a (also referred to as the “sensingrange” of the worksurface 102 a). As used herein, this measured distance(or measured characteristic indicative of the distance) is also referredto as the “measured worksurface Z-height.” In addition, when a Z-heightsensor 124 is configured to measure a distance (or a characteristicthereof) between a particular scan lens 112 and a region of theworksurface 102 a, the Z-height sensor 124 may also be described as aZ-height sensor that is associated with the particular scan lens 112 (orwith a particular scan head incorporating the scan lens) or, moresimply, as an “associated Z-height sensor.” The Z-height sensor 124 maybe provided as any suitable or beneficial displacement sensor, distancesensor, position sensor, or the like or any combination thereof.Examples of sensors that may be used as the Z-height sensor 124 includea laser triangulation sensor, a laser profile sensor, a scanningconfocal laser sensor, a confocal interference displacement sensor, anair gauge sensor, or the like or any combination thereof.

In one embodiment, the Z-height sensor 124 is positionally fixedrelative to its associated scan lens 112 (e.g., the Z-height sensor 124is coupled to the scan head 118, scan lens housing, etc., or is coupledto a frame to which the scan head 118 is coupled). In this case, theposition of the sensing range relative to the second scanning range(e.g., as measured in the X-Y plane) is fixed. In another embodiment,the apparatus 100 is configured such that the Z-height sensor 124 andthe scan lens 112 are moveable relative to one another. For example, theZ-height sensor may be movable (e.g., in the X-, Y- or Z-directions, orthe like or any combination thereof) relative to the scan lens 112(e.g., the Z-height sensor 124 is coupled to a linear or rotationalstage that, in turn is coupled to the scan head 118 or to some otherframe, bracket, rail, etc., associated with the apparatus 100). Inanother embodiment, the Z-height sensor 124 may be positionally fixedwithin the apparatus 100, and the scan lens 112 may be movable (e.g., inthe X-, Y- or Z-directions, or the like or any combination thereof)relative to the Z-height sensor 124.

The Z-height sensor 124 can generate one or more signals (e.g.,“Z-height signals”), data (e.g., Z-height data), or the like or anycombination thereof (generically and collectively referred to as“Z-height information”) indicative of the measured worksurface Z-height,and output the same to the controller 114. In its raw form, Z-heightinformation generated or output from the Z-height sensor 124 can benoisy. Sometimes, the noise can be too large to form a reliable basisfor determining whether or not the worksurface Z-height is outside apredetermined nominal Z-height process window (e.g., ±60 μm, ±70 μm, ±80μm, ±90 μm, ±100 μm, or the like) relative to a reference worksurfaceZ-height. If the “raw” Z-height information is too noisy, then it can beprocessed (e.g., filtered, smoothed, or the like or any combinationthereof) at the Z-height sensor 124, at the controller 114, or the likeor any combination thereof, to obtain a “processed” worksurfaceZ-height, which can form the basis for determining whether or not theworksurface Z-height is outside the predetermined nominal Z-heightprocess window.

In one embodiment, items of raw or processed Z-height information arestored (e.g., in a data structure conveyed by computer memory such as abuffer or cache of the controller 114). Each item of Z-heightinformation may be stored in association with a corresponding item ofinformation indicating a position of the sensing range relative to thethird scanning range (also referred to herein as a “sensing position”)when a Z-height measurement associated with the item Z-heightinformation was obtained. Information indicative of sensing position canbe obtained or derived (e.g., at the controller 114) from one or moresignals (e.g., encoder signals) generated and output by the thirdpositioner 110 to the controller 114, and can be given in terms ofposition along the X-, Y- or Z-directions, or any combination thereof.

Generally, the interval between sensing positions can depend upon one ormore factors such as the workpiece 102 to be processed, the type ofprocessing to be performed, the location where a feature is to be formedon or within the workpiece 102, the desired precision or accuracy withwhich a feature is to be formed on or within the workpiece 102, or thelike or any combination thereof. In embodiment, the interval betweensensing positions is in range from 0.1 mm to 6 mm (e.g., in a range from0.2 mm to 5 mm). In another embodiment (e.g., in which the workpiece 102is a PCB, and the processing involves via drilling), the intervalbetween sensing positions is in a range from 0.5 mm to 1.5 mm (e.g., 1mm, or thereabout). It will be appreciated, however, that the intervalbetween sensing positions may be less than 0.1 mm or greater than 6 mm.The interval between two pairs of adjacent sensing positions may beconstant, or may be variable. In one embodiment, Z-height measurementscan be triggered in response to a control signal received from thecontroller 114 (e.g., that, in turn, is generated and output uponreceiving one or more encoder signals output by the third positioner110, etc.), in response to one or more encoder signals received from thethird positioner 110, or the like or any combination thereof.

In another embodiment, an item of Z-height information (and itsassociated position information) is stored only if it indicates that aworksurface Z-height is outside the predetermined nominal Z-heightprocess window. In this embodiment, the controller 114 can be configuredto process the Z-height information to determine whether or not theworksurface Z-height (e.g., either as measured or processed) at aparticular position is outside the predetermined nominal Z-heightprocess window (and store the Z-height information and positioninformation when the determination is answered in the affirmative). Inanother embodiment, the Z-height sensor 124 can be configured to processthe Z-height information to determine whether or not the worksurfaceZ-height (e.g., either as measured or processed) is outside thepredetermined nominal Z-height process window (and output the Z-heightinformation to the controller 114 when the determination is answered inthe affirmative).

If the worksurface Z-height (e.g., either as measured or processed) isdetermined (e.g., by the controller 114 or the Z-height sensor 124) tobe outside the predetermined nominal Z-height process window, then thecontroller 114 can generate and output one or more control signals tothe lens actuator, the third positioner 110, or the like or anycombination thereof to compensate for the detected variation ordeviation outside the predetermined nominal Z-height process window(e.g., so that a delivered laser pulse will have a desired spot size atthe desired process spot). Z-height compensation can be effected byoutputting one or more control signals to actuate one or more mechanismsfor effecting Z-height compensation so that a delivered laser pulse willhave a desired spot size at the desired process spot. Examples ofmechanisms for effecting Z-height compensation, which may be used inembodiments provided herein, are discussed in greater detail below.

It is straightforward to effect realtime Z-height compensation if theworksurface Z-height is already known. However, the worksurface Z heightmay not be known (or may not be known to the required precision) beforethe workpiece 102 is processed. In one embodiment, the worksurfaceZ-height at all positions where the workpiece 102 is to be processed ismeasured before laser processing of the workpiece 102 begins. However,such “offline” measurement of worksurface Z-height can require too muchtime or expense when the workpiece 102 is large. This is especially trueif the anticipated time required to complete the laser-processing isrelatively short, if the sensed range for the Z-height sensor is smallrelative to the size of the workpiece 102, etc. Also, variation in theworksurface Z-height can be large enough to render intendedlaser-processes incapable of meeting specified quality requirements.Therefore, it may be preferable to measure the worksurface Z-height inrealtime, during workpiece processing, instead of prior to workpieceprocessing.

To facilitate realtime worksurface Z-height measurement, the Z-heightsensor 124 can be arranged and configured such that the sensing range isarranged within the second scanning range 302 b (e.g., either partiallywithin or completely within the second scanning range 302 b, such that acentroid or other central region of the sensing range is within oroutside the second scanning range 302 b). Accordingly, compensation forthe detected variation or deviation in worksurface Z-height can, in oneembodiment, be effected immediately upon determining that the detectedvariation or deviation is outside the nominal Z-height process window.It is possible, however, that the response time associated with amechanism for effecting Z-height compensation will be excessively longand, as a result, will need to be compensated for (e.g., by delaying thelaser processing sequence until the detected variation or deviation inworksurface Z-height has been compensated). Delays due to response timeof mechanisms for effecting Z-height compensation are hereinafterreferred to as “response time delays.” It is also possible that theprocessing of raw Z-height information (e.g., to obtain a “processed”worksurface Z-height) can also be a source of delay (also referred to asa “processing delay”) that may need to be similarly compensated for.However if response time and processing delays are relatively smallcompared to the rate with which the second scanning range is movedrelative to the workpiece (or vice versa), then such delays need not becompensated for.

In some cases, it may be difficult to obtain accurate worksurfaceZ-height measurements when the sensing range is arranged within thesecond scanning range 302 b as described above. Therefore, in otherembodiments, the Z-height sensor 124 can be arranged and configured suchthat the sensing range lies completely outside the second scanning range302 b. For example, and with reference to FIGS. 4 to 6, the Z-heightsensor 124 is arranged and configured such that the sensing range 402 isoffset from the second scanning range 302 b along the Y-direction (e.g.,as shown in FIG. 4), along the X-direction (e.g., as shown in FIG. 5),or along X- and Y-directions (e.g., as shown in FIG. 6.). Although FIGS.4 to 6 illustrate the sensing range 402 is offset from the secondscanning range 302 b in the −X-direction, the −Y-direction, or the −Xand −Y-directions, it will be appreciated that the sensing range 402 canbe offset from the second scanning range 302 b in any of the −X, +X, −Y,or +Y-directions, or any combination thereof. In the embodimentsillustrated in FIGS. 4 and 6, the distance or pitch p(y) between thesecond scanning range 302 b and the sensing range 402 along theY-direction (i.e., as measured from the centers of each of these regionsalong the Y-direction) is equal to the distance d′(y) of the secondscanning range 302 b. Likewise, in the embodiments illustrated in FIGS.5 and 6, the distance or pitch p(x) between the second scanning range302 b and the sensing range 402 along the X-direction (i.e., as measuredfrom the centers of each of these regions along the X-direction) isequal to the distance d′(x) of the second scanning range 302 b. In otherembodiments however, the distances p(y) and p(x) may be greater than, orless than, corresponding distances d′(y) and d′(x), respectively.

In the examples discussed with respect to FIGS. 4 to 6, the sensingrange 402 is, generally, circular in dimension, with a diameter of in arange from 1 mm to 3 mm. In one embodiment, the sensing range 402 has adiameter in a range from 1.5 mm to 2 mm. It will be appreciated,however, that the sensing range 402 may have a diameter that is lessthan 1 mm or greater than 3 mm. For example, the sensing range 402 mayhave a diameter equal to, or greater than, any of aforementioneddistances d(x), d′(x), d(y) or d′(y). In other example embodimentshowever, instead of having a circular shape, the shape of the sensingrange 402 may, generally, be triangular, square, rectangular,elliptical, etc. In yet another example embodiment, the shape and sizeof the sensing range 402 may, generally, be same as the shape and sizeof the second scanning range 302 b. In one embodiment, the Z-heightsensor 124 is configured to generate Z-height information indicative ofthe average or mean worksurface Z-height measured within the sensingrange 402. In another embodiment, the Z-height sensor 124 is configuredto generate Z-height information indicative of the actual, average ormean worksurface Z-height measured at a plurality of points within thesensing range 402.

In view of the above, placement of the sensing range 402 relative to thesecond scanning range 302 b (e.g., which can be characterized by thedirection in which the sensing range 402 is offset from the secondscanning range 302 b, by the pitch between the sensing range 402 and thesecond scanning range 302 b, or the like or any combination thereof) canbe flexible. For example, placement of the sensing range 402 relative tothe second scanning range 302 b can correspond to the relative motion ofthe second scanning range 302 b and the workpiece 102 during laserprocessing. Such relative motion can be characterized by parameters suchas speed of movement, direction of movement—which may proceed along theX- or Y-directions, or one or more directions other than the X- andY-directions, or any combination thereof, etc.

Thus in one embodiment, the sensing range 402 may be offset relative tothe second scanning range 302 b in a direction that is different fromthe direction in which the second scanning range 302 b is caused to moverelative to the workpiece 102 (e.g., upon moving the scan lens 112, theworkpiece 102, or a combination thereof, by actuating the thirdpositioner 110). For example, the sensing range 402 may be offset fromthe second scanning range 302 b in the −X-direction (e.g., as shown inFIG. 5 or 6) or in the +X-direction if, during the intended laserprocessing, the second scanning range 302 b is caused to move relativeto the workpiece 102 in the +Y or −Y-directions. Offsetting the sensingrange 402 in this manner can provide for realtime worksurface Z-heightmeasurement but is also susceptible to the same response time andprocessing delays discussed above. Also, offsetting the sensing range402 as described above can problematic if laser processing is performedat an edge of the workpiece 102 and the sensing range 402 is either notlocated on the workpiece 102, or is located only partially on theworkpiece 102. However these problems (or susceptibility to problems)can be ameliorated or avoided by implementing, when processing theworkpiece 102, a scanning technique according to one or more embodimentsexemplarily described below.

In another embodiment, the sensing range 402 may be offset relative tothe second scanning range 302 b in a direction that is the same as thedirection in which the second scanning range 302 b is caused to moverelative to the workpiece 102 (e.g., upon moving the scan lens 112, theworkpiece 102, or a combination thereof, by actuating the thirdpositioner 110). For example, the sensing range 402 may be offset fromthe second scanning range 302 b in the −Y-direction (e.g., as shown inFIG. 4 or 6) if, during the intended laser processing, the secondscanning range 302 b is caused to move relative to the workpiece 102 inthe −Y-direction. Offsetting the sensing range 402 in this manner canprovide for realtime worksurface Z-height measurement but is alsosusceptible to the same delays discussed above. Also, and depending onthe workpiece 102 being processed, offsetting the sensing range 402 asdescribed above will often (though, not necessarily always) only beeffective if the sensing range 402 is offset in the same direction inwhich the second scanning range 302 b is caused to move relative to theworkpiece 102. This problem, however, can be mitigated by providingmultiple Z-height sensors (e.g., configured and arranged so as to yieldmultiple sensing ranges, each disposed on opposite sides of the secondscanning range 302 b). This problem, can also be mitigated byimplementing, when processing the workpiece 102, a scanning techniqueaccording to one or more embodiments exemplarily described below.

In embodiments in which the centroid or other central region of thesensing range 402 is arranged completely outside the second scanningrange 302 b, the controller 114 compensates for the detected variationor deviation indicated by an item of Z-height information when aprocessing position is the same as the sensing position associated withthat item of Z-height information. In another embodiment, compensationfor the detected variation or deviation is effected when the processingposition is within a specified distance (e.g., within 400 μm, 200 μm,100 μm, 80 μm, 60 μm, 50 μm, 30 μm, 15 μm, or the like, etc.) of thesensing position. The specified distance may be fixed, or may bevariable depending upon factors such as the rate with which the secondscanning range 302 b is scanned, the response time associated with themechanism for effecting Z-height compensation, or the like or anycombination thereof. Such compensation may likewise be effected inembodiments in which the centroid or other central region of the sensingrange 402 is within the second scanning range 302 b, or in which thesensing range 402 is arranged partially within the second scanning range302 b but the centroid or other central region of the sensing range 402is outside the second scanning range 302 b.

The processing position can be a position (e.g., determined relative tothe third scanning range) where a current laser pulse is to be deliveredto a process spot during processing of the workpiece, a centroidposition corresponding to positions where a series of laser pulses to besequentially-delivered to a plurality of spatially distributed processspots during processing of the workpiece, a portion of the secondscanning range 302 b (e.g., an edge thereof, a centroid or otherinterior region thereof), a portion of the first scanning range (e.g.,an edge thereof, a centroid or other interior region thereof), or thelike or any combination thereof. Information indicative of theprocessing position can be obtained or derived (e.g., at the controller114) from one or more signals (e.g., encoder signals) generated andoutput to the controller 114 by the first positioner 106, the secondpositioner 108, the third positioner 110, or any combination thereof,from information describing the process trajectory, or the like or anycombination thereof.

Although particular embodiments in this section concerning the placementof the sensing range 402 have been discussed in relation to the secondscanning range 302 b, it will be appreciated that the Z-height sensor124 may, in other embodiments, be arranged and configured such that thesensing range 402 is similarly offset from other scanning ranges such assecond scanning range 302 a. Further, although particular embodiments inthis section concerning Z-height have been discussed in connection withthe apparatus 100, it will be appreciated that any one of theseembodiments, or any combination thereof, may be implemented inconnection with any laser-processing apparatus other than the apparatus100. Further, although particular embodiments in this section concerningZ-height measurement and Z-height compensation, etc., have beendiscussed in connection with laser-processing apparatus and laser-basedprocesses, it will be appreciated that any one of these embodiments orany combination thereof, may be implemented in connection with any othersuitable apparatus such as a mechanical drill, water-cutting or drillingapparatus, electron-beam cutting machines, abrasive blasting machines,etc. configured to process a workpiece.

A. Example Embodiments of Mechanisms for Effecting Z-Height Compensation

i. Lens Actuator

In one embodiment, a mechanism for effecting Z-height compensation mayinclude the aforementioned lens actuator. For example, the lens actuatorcan be actuated to adjust the location of the beam waist along the beamaxis (also referred to herein as the “focus Z-height,” as measured fromthe exit pupil of the scan lens 112), so that a delivered laser pulsewill have a desired spot size at the desired process spot.

ii. First Positioner

In one embodiment, the first positioner 106 may include a MEMS mirror ormirror array, as exemplarily described above, which can be actuated toeffect Z-height compensation by changing the spot shape or spot size oflaser pulses delivered to the workpiece 102. In another embodiment, thefirst positioner 106 may include one or more AOD systems, as exemplarilydescribed above, which can be driven (e.g., upon the application of oneor more RF signals to one or more ultrasonic transducer elements, eachacoustically coupled to one or more AO cells) to effect Z-heightcompensation. Example embodiments of driving an AOD system are describedin greater detail below. Although these example embodiments arediscussed in relation to an AOD system incorporated within an apparatussuch as apparatus 100 or 700, it will be appreciated that the exampleembodiments may be suitably implemented with any laser-based apparatusincorporating an AOD system, regardless of whether the laser-basedapparatus is a laser-processing apparatus.

a. Chirped RF Signals

In one embodiment, when the first positioner 106 includes an AOD system(e.g., a multi-axis AOD system), the AOD system can be driven bychirping an RF signal applied to one or more ultrasonic transducerelements of the AOD system when laser pulses transit through an AO cellacoustically coupled thereto. Chirping an applied RF signal has theeffect of creating a change in the focal length of the beam of laserpulses exiting the AOD system. Upon changing the focal length, theeffective spot size of laser pulses delivered to the workpiece 102changes in a corresponding manner. The degree to which the focal lengthis changed can be characterized by the following:F=v ²/(λ*df/dt),where F is the effective focal length produced by the chirping, v is theacoustic velocity within the AO cell, λ is the wavelength of laserpulses and df/dt is the rate of change in the RF frequency applied tothe ultrasonic transducer element. As will be appreciated, the directionin which the focal length is changed (i.e., toward or away from theworkpiece 102) is given by the sign of F (i.e., which may be positive ornegative, depending on whether the frequency is modulated to increase ordecrease with time).

Generally, chirping an applied RF signal works well for laser pulsesthat are shorter than the transit time of the acoustic wave through theaperture illuminated by the beam of laser pulses. It can be difficult toeffectively change the focal length of a beam of laser pulses generatedby a laser source 104 such as a QCW laser, essentially because QCWlasers have (effectively) no laser-off time between pulses during whichthe chirp frequency can be reset to a starting value. Accordingly, itcan be easier to implement a chirping technique with discretely-pulsedlasers, such that the chirp sweep (about center AOD frequencies requiredfor spot positioning) can be set up properly as the laser pulse passesthrough the AOD. Nevertheless, chirping techniques can be used with CWor QCW lasers if a pulse gating unit is also provided.

The extent to which an AOD system can impart movement to the beam axisis proportional to the frequency of the applied RF signal. When theapplied RF frequency is chirped, the acoustic wave frequency will varyacross the width of a laser pulse (i.e., measured transverse to the beampath 116) transiting through the AO cell, and deflection of the beampath 116 will be proportional to the mean frequency across thetransiting laser pulse. The mean frequency can be properly set up orcalibrated to impart desired movement of the beam axis. However,variations in laser pulse and/or AOD control signal timing can cause ashift in this mean frequency, and thus create a spot position error(i.e., resulting in a laser pulse being delivered to a position at theworkpiece 102 that is different from the desired spot location). Forexample, an AOD system have a first scanning range of 150 μm (e.g., overa 30 MHz bandwidth). Thus the amount of beam path deflection per MHzwould be 150 μm/30 Mhz, or 5 μm/MHz. If a desired chirp rate is 30MHz/μs, a timing variation of 10 ns would produce a beam path deflectionerror of 1.5 μm (i.e., (5 μm/MHz)*(30 MHz/μs)*(10 ns)).

The variation in laser pulse and/or AOD control signal timing typicallyarises from circuitry or operations within the controller 114 (as it maybe variously embodied), variations in drivers, generation of laserpulses from the laser source 104, etc. In some laser sources (such asdiode-pulsed fiber lasers), the jitter between an input laser triggersignal and the corresponding laser pulse ultimately generated may berelatively low (<10 ns). In other laser sources (e.g. Q-switcheddiode-pump lasers), the variation may be larger (e.g., due to randomsynchronization of internal Q switch activity and laser cavitydynamics). For instance, a typical UV Q-switched laser can exhibitapproximately ±15 ns of timing uncertainty between the input lasertrigger signal and the corresponding laser pulse ultimately generated.Further, a typical FPGA may have a fundamental clock running at a 20 nsclock period. Thus a controller 114 including such an FPGA wouldintroduce an additional ±10 ns of timing uncertainty. These timinguncertainties can result in a positioning error for laser pulsesultimately delivered to the workpiece 102 (i.e., a variation ordeviation of the actual location of where the laser pulse is ultimatelydelivered away from the desired process spot). Depending on theparticular features to be formed during processing, this positioningerror may or may not be significant.

When effecting Z-height compensation, the above-described positioningerror may be significant. In such situations, synchronization betweenthe output of a trigger signal to the laser source 104 (e.g., togenerate a laser pulse), the output of a trigger signal to the AODsystem (e.g., to apply one or more chirped RF signals), and generationof laser pulses by the laser source 104 may be improved. For example, inan embodiment in which the laser source 104 relies on an internal clockto trigger the output of laser pulses, the internal clock could besynchronized (e.g., through a PLL, gating logic, etc.) to the internalclock of the controller 114 that initiates the trigger signal to the AODsystem. Further, any clock involved in generating the chirp sequenceitself (e.g., a clock used by a direct digital synthesizer (DDS)circuit, etc.) may be similarly synchronized. This synchronization canreduce the timing uncertainty to only the timing uncertainty due torandom laser cavity effects.

b. Spectrally-Shaped RF Signals

In one embodiment, when the first positioner 106 includes an AOD system(e.g., a multi-axis AOD system), the AOD system can be driven byapplying a spectrally-shaped RF signal to one or more ultrasonictransducer elements when laser pulses transit through an AO cellacoustically coupled thereto. In this embodiment, the shape of thespectrum in the applied RF signal is selected to change the M² factor(also known in the art as the “beam quality factor” or “beam propagationfactor”) of the beam of laser pulses exiting the AOD system. Uponchanging the M² factor, the effective spot size of laser pulsesdelivered to the workpiece 102 changes in a corresponding manner. Thedegree to which the M² factor can be changed corresponds to the breadthof the spectrum in the applied RF signal (e.g., a relatively broadspectrum will have a stronger impact on the M² factor than a relativelynarrow spectrum). Generally, shaping the spectral content of an appliedRF signal—as described herein—works well for laser pulses that arelonger than the transit time of the acoustic wave through the apertureilluminated by the beam of laser pulses.

In embodiments in which laser pulses having a radially-symmetric,Gaussian spatial intensity profile are to be delivered to the workpiece102 (and assuming that laser pulses output by the laser source 104 havea Gaussian spatial intensity profile), then the spectrum of the appliedRF signal can also have a Gaussian shape. In one embodiment, therefore,a first type of RF signal that may be applied can characterized as arelatively narrow signal spiking in the time domain (i.e., implying aconstant, or substantially constant, phase between all frequencies inthe applied signal spectrum). This type of signal has the potential tonegatively affect the overall diffraction efficiency of the AOD cell.Accordingly, in another embodiment, a second type of RF signal that maybe applied can be characterized as a relatively smooth signal, lookingalmost like a single frequency oscillation (e.g., a signal where theamplitude of one oscillatory peak is approximately the same as theamplitude of every other oscillatory peak). Such an RF signal caninclude a quasiperiodic signal. Unlike spiked RF signals, thesespectrally-shaped RF signals can be constructed to not noticeably impactthe diffraction efficiency of the AO cell.

Suitable spectrally-shaped RF signals can be created using any suitabletechnique. In one embodiment, a spectrally-shaped RF signal can becreated by a process that includes selecting a desired center frequency,ω_(o), to set the centroid position of the modulated beam, selecting thedesired spectral width, σ_(ω), to set the effective laser pulse spotsize at the workpiece 102, selecting a desired frequency resolution,r_(ω), to set the spacing of discrete frequencies to be driven, andinputting the selected center frequency, ω_(o), spectral width, σ_(ω)and frequency resolution, r_(ω), to an algorithm such as theGerchberg-Saxton algorithm, to approximate, the desired spectralproperties for an RF signal to be applied, through determination of thephases needed for each frequency. In this embodiment, the AOD system canbe designed such that the beam of laser pulses incident upon AO cellilluminates a relatively large number of grating periods of the AO cell(e.g., a 6 mm beam size incident upon a quartz AO cell at a pulserepetition rate of 100 MHz illuminates more than 100 periods), therebyachieving a suitable approximation to a Gaussian spectrum for mostpractical cases. The approximation can then be applied (e.g., at thecontroller 114) to generate one or more appropriate spectrally-shaped RFsignals to be applied to the AOD system. By varying the spectral width,σ_(ω), input to the approximation algorithm, the spectrum of the appliedRF signal can be varied to vary the width of the spectrum in the appliedRF signal. Further, the beam path 116 can be deflected by varying thecenter frequency, ω_(o), input to the approximation algorithm. It willthus be appreciated that the spectral width, σ_(ω), center frequency,ω_(o), and frequency resolution, r_(ω), or any combination thereof canbe varied either together or separately.

iii. Third Positioner

In another embodiment, a mechanism for effecting Z-height compensationmay include the third positioner 110. For example, the third positioner110 can be actuated to move the workpiece 102 so that the worksurfaceZ-height is within the predetermined nominal Z-height process window(thereby enabling the beam waist of a delivered laser pulse to bepresent at the desired process spot).

iv. Other Example Embodiments of Mechanisms for Effecting Z-HeightCompensation

In one embodiment, a mechanism for effecting Z-height compensation mayinclude a component such as a lens, a MEMS mirror or mirror array, orthe like or any combination thereof. In this embodiment, such amechanism may be provided (e.g., in addition to the first positioner106, the third positioner 110, the scan lens 112 or any combinationthereof), and may be disposed in the beam path 116 at any locationoptically “upstream” or “downstream” of the first positioner 106, thesecond positioner 108, the third positioner 110, the scan lens 112, orany combination thereof. When provided as a lens, the lens may beprovided as a fixed-focal length lens coupled to a lens actuator (e.g.,a voice coil, etc.) configured to translate the lens along the beam path116, thereby effecting a change in position of the beam waist along thebeam axis. In another embodiment, the lens may be provided as avariable-focal length lens (e.g., a zoom lens, or a so-called “liquidlens” incorporating technologies currently offered by COGNEX, VARIOPTIC,etc.) capable of being actuated (e.g., via a lens actuator) to changethe position of the beam waist along the beam axis.

V. Embodiments Concerning Scan Head Configurations

In the embodiment shown in FIG. 1, the apparatus 100 includes a singlescan head 118. In another embodiment, however, the apparatus 100 may beprovided with multiple (e.g., 2, 3, 4, 5, 6, 8, etc.) scan heads, eachof which may or may not be provided in the manner described with respectto scan head 118. Providing an apparatus 100 with multiple scan heads(i.e., as a “multi-head apparatus”) may improve the throughput of laserprocesses applied by the apparatus 100. Different scan heads of such amulti-head apparatus can be identically or differently mounted,configured, driven, actuated, or the like or any combination thereof.

For example, in one embodiment, one or more characteristics of scanlenses of different scan heads can be the same or different. Examplecharacteristics of a scan lens can include type (e.g., f-theta,telecentric, axicon, etc.), focal length, numerical aperture, materialcomposition, presence/absence of coatings, coating composition, etc.

In another example, a positioner (e.g., the aforementioned secondpositioner 108) may be incorporated within a scan head, while anotherscan head may or may not have a positioner incorporated therein orotherwise associated therewith. Moreover, one or more characteristics ofpositioners of different scan heads can be the same or different.Example characteristics of positioners can include the number ofpositioners (e.g., 1, 2, 3, etc.) of a scan head 702, the type (e.g., amechanical-type positioner such as a galvanometer mirror, MEMS mirror ormirror array, a piezoelectric actuator, an electrostrictive actuator, avoice-coil actuator, etc., a solid-state positioner such as an AOD, anEOD, etc.) of each positioner of a scan head, positioning bandwidth,size of scanning range, shape of scanning range, manufacturer, softwarecontrol, etc. Likewise, a positioner of one scan head 702 can be drivenaccording to the same control signal(s) as a positioner of one or moreother scan heads 702. Alternatively, a positioner of one scan head 702can be driven according to a different control signal as a positioner ofone or more other scan heads 702.

In one embodiment, different scan heads can be mounted within theapparatus in the same way, or in different ways. For example, at leastone (or all) scan heads can be fixed (e.g., to a frame incorporatedwithin the apparatus) so as to remain stationary within the apparatus.In another example, at least one (or all) scan head can be moveablewithin the apparatus. When moveable, at least two (or all) scan headsmay be moveable (e.g., linearly translated, rotated, etc.) in or alongthe same direction, in or along different directions, or the like or anycombination thereof. When configured to be moveable in the samedirection, the at least two (or all) scan heads may be moveable at thesame speed (e.g., such that no relative movement occurs as between thosescan heads) or at different speeds (e.g., such that relative movementoccurs as between those scan heads). To facilitate movement, theapparatus may include one or more gantries, linear stages, rotationalstages, articulated robotic arms, or the like or any combinationthereof, beneficially coupled to one or more of the scan heads. Suchstages may be part of the aforementioned third positioner 110 (and thusdriven according to one or more control signals intended to impartrelative movement between the beam axis and the workpiece 102, asdiscussed above), or may be separate from the third positioner 110 (andthus driven according to one or more control signals intended for somepurpose other than impart relative movement between the beam axis andthe workpiece 102, e.g., to ensure adjust an alignment between each scanhead and one or more workpieces to be processed by the multi-headapparatus).

In some embodiments, the multi-head apparatus can include a singleZ-height sensor, such as the aforementioned Z-height sensor 124, or mayinclude multiples of such Z-height sensors. In some embodiments, aZ-height sensor may be associated with a single scan head, or may beassociated with multiple (e.g., 2, 3, 4, 5, 6, 8, etc.) scan heads. Inone embodiment, the number of Z-height sensors included is the same asthe number of scan heads in the multi-head apparatus, and each Z-heightsensor is associated with a single scan head.

Having described certain features of a multi-head apparatus above,configurations associated with the multi-head apparatus according tosome embodiments will be exemplarily described in greater detail withreference to FIG. 7.

When provided as a multi-head apparatus, the apparatus 100 (referred towith respect to FIG. 7 as a multi-head apparatus 700) may include fourscan heads, such as first scan head 702 a, second scan head 702 b, thirdscan head 702 c and fourth scan head 702 d (each generically referred toas a scan head 702 or, collectively, scan heads 702). Groups of scanheads 702 can be supported by a common rail. For example, first scanhead 702 a and third scan head 702 c can be commonly supported by afirst rail 704 a and the second scan head 702 b and fourth scan head 702d can be commonly supported by a second rail 704 b. As used herein, thefirst rail 704 a and the second rail 704 b are also generically referredto as a rail 704 or, collectively, as rails 704.

Generally, each rail 704 can be fixed within the apparatus 100 so as tobe stationary or moveable (e.g., linearly translated along theX-direction, along the Y-direction, or along some other direction, orabout an axis parallel to the X- or Y-directions, or rotated about anaxis parallel to some other direction, or the like, or any combinationthereof). For example, in the illustrated embodiment, the first rail 704a may be coupled to a stage (not shown) configured to move the firstrail 704 a along the X-direction (e.g., as indicated by arrow 706), andthe second rail 704 b fixed within the multi-head apparatus 700 so as tobe stationary.

Generally, scan heads 702 carried by a rail 704 can be coupled to therail 704 so as to be stationary or moveable (e.g., linearly translatedalong the X-direction, along the Y-direction, or along some otherdirection, or about an axis parallel to the X- or Y-directions, orrotated about an axis parallel to some other direction, or the like, orany combination thereof). For example, in the illustrated embodiment,the third scan head 702 c and the fourth scan head 702 d are fixed so asto be stationary with respect to the first rail 704 a and the secondrail 704 b, respectively, whereas the first scan head 702 a is coupledto a first Y-stage 708 a (which may also be carried by the first rail704 a) so as to be movable along the Y-direction (e.g., as indicated byarrow 710) and the second scan head 702 b is coupled to a second Y-stage708 b (which may also be carried by the second rail 704 b) so as to bemoveable along the Y-direction (either independently of, or in unisonwith, the first scan head 702 a). Alternatively, the first scan head 702a and second scan head 702 b may be coupled to a common Y-stage (notshown) that moveably coupled to the first rail 704 a and/or second rail704 b (e.g., via any suitable or beneficial mechanical linkage spanningthe first rail 704 a and second rail 704 b). Thus, constructed asdescribed above, the first scan head 702 a is moveable along the X- andY-directions, the second scan head 702 b is moveable along theY-direction (e.g., in unison with the first scan head 702 a), the thirdscan head 702 c is moveable along the X-direction (e.g., in unison withthe first scan head 702 a), and the fourth scan head 702 d is fixed soas to remain stationary.

Generally, each scan head 702 is adapted to receive laser pulses thatpropagate along one or more beam paths, such as aforementioned beam path116, from one or more laser sources such as such as aforementioned lasersource 104. For example, in the illustrated embodiment, the laser pulsesare generated from a single laser source 104, and are modified (e.g.,focused, expanded, collimated, shaped, polarized, filtered, split, orotherwise modified, conditioned or directed, etc.) by an optionaloptical system 712. The optical system 712 may include one or moreoptical components including a beam expander, a beam shaper, anaperture, a harmonic generation crystal, a filter, a collimator, a lens,a mirror, a polarizer, a diffractive optical element, a refractiveoptical element, or the like or any combination thereof. In oneembodiment, the optional optical system 712 may include anyconfiguration of optical components as exemplarily described in thecontext of modular imaging optical rails in U.S. Pat. No. 6,433,301,which is incorporated herein by reference in its entirety.

In the illustrated embodiment, the laser pulses generated by the lasersource 104 (and, optionally, passed by the optical system 712) arepropagated through a primary beam distributor 714 to direct,simultaneously and/or alternately, laser pulses along a first primarybeam path 116 a 1 and a second primary beam path 116 a 2 (eachgenerically referred to as a primary beam path 116 a or, collectively,primary beam paths 116 a). In one embodiment, the primary beamdistributor 714 is provided as an AOM, and the primary beam paths 116 aare provided as zeroth- and first-order beam paths associated with theAOM (e.g., as exemplarily discussed in aforementioned U.S. Pat. No.7,133,187). Generally, diffraction efficiency of an AOM is not 100%.Therefore, at least some energy will always be transmitted along aprimary beam path 116 a, even when the AOM is driven to select thefirst-order beam path. Accordingly, and in an optional embodiment,energy transmitted along the zeroth-order beam path can be blocked orotherwise prevented from reaching the worksurface 102 a by suitablyoperating the first positioner 106, the second positioner 108, or thelike or any combination thereof. In another embodiment, however, one ofthe primary beam paths 116 a may be provided as a positive first-orderbeam path associated with the AOM and the other of the primary beampaths 116 a may be provided as a negative first-order beam pathassociated with the AOM. In this embodiment, a beam dump (not shown) maybe provided to receive energy transmitted along the zeroth-order beam ofthe AOM.

When provided as an AOM, the primary beam distributor 714 may,optionally, be operated (e.g., in response to one or more controlsignals output by the controller 114, by another controller, or the likeor any combination thereof), to temporally chop or slice the laserpulses generated by the laser source 104 (and, optionally, passed by theoptical system 712), to block, dump or otherwise attenuate one or morelaser pulses (in their entirety) generated by the laser source 104 (and,optionally, passed by the optical system 712), or the like or anycombination thereof. For example, the AOM may be operated to block, dumpor otherwise attenuate at least one portion of one or more (or all)laser pulses generated by the laser source 104 (and, optionally, passedby the optical system 712). One or more portions of a laser pulse may beblocked, dumped or otherwise attenuated to generate one or more laserpulses having a relatively reduced pulse duration, shorter or longerrise time, shorter or longer fall time, or the like or any combinationthereof.

Blocking or dumping one or more laser pulses in a series ofsequentially-generated laser pulses is also known as “pulse picking.”Pulse picking may be implemented whenever suitable or otherwise desired.For example, if a processing trajectory required to form a plurality offeatures (e.g., vias) specifies that at least some of thefeature-to-feature moves to be traversed by the process spot will takethe same amount of time, Tm, then laser pulses can be generated by thelaser source 104 at a pulse repetition rate of 1/Tm. Then, for anyfeature-to-feature moves that are to be traversed by the process spotover an amount of time that is an integer multiple, k, of Tm (e.g.,k*Tm), then the primary beam distributor 714 (e.g., when provided as anAOM) can be operated to block any pulses generated during the period ofk*Tm.

In some cases, a change in the pulse repetition rate with which laserpulses are generated by the laser source 104 ends up changing thetemporal intensity profile of the generated laser pulses in a measurableway. Such changes can be characterized (e.g., during a pre-processingcalibration step, etc.) and the primary beam distributor 714 (e.g., whenprovided as an AOM) can be operated to compensate for thosepre-characterized changes (e.g., by blocking, dumping or otherwiseattenuating at least one portion of one or more (or all) laser pulsesgenerated by the laser source 104). As a result, laser pulsespropagating along the primary beam paths 116 a can have uniform (or atleast substantially uniform) temporal intensity profiles, regardless ofa change in pulse repetition rate with which the laser pulses aregenerated.

In other embodiments, the primary beam distributor 714 may be providedas one or more polarizers, beam splitters, spinning chopper mirrors,rotating polygon mirrors, resonant galvanometer mirror systems,electro-optic modulators (EOMs), or the like or any combination thereof.The use of EOMs for controlling alternative beam paths and/or combiningbeam paths is discussed in detail in U.S. Pat. No. 8,374,206, which isincorporated herein by reference in its entirety. It also will beappreciated that the optional optical system 712 may be commonlydisposed along the primary beam paths 116 a at a location downstream ofthe primary beam distributor 714, instead of upstream of the primarybeam distributor 714 as illustrated. In other embodiment, a plurality ofoptional optical systems 712 may be provided downstream of the primarybeam distributor 714, with each optional optical system 712 beingpositioned along a different primary beam path 116.

Laser pulses directed along the primary beam path 116 a are furtherdistributed by a first secondary beam distributor 716 a and a secondsecondary beam distributor 716 b (each generically referred to as asecondary beam distributor 716 or, collectively, secondary beamdistributors 716). The first secondary beam distributor 716 a isconfigured to direct, simultaneously and/or alternately, laser pulsespropagating along the first secondary beam path 116 a 1 to a firstsecondary beam path 116 b 1 and a second secondary beam path 116 b 2.Likewise, the second secondary beam distributor 716 b is configured todirect, simultaneously and/or alternately, laser pulses propagatingalong the second secondary beam path 116 a 2 to a third secondary beampath 116 b 3 and a fourth secondary beam path 116 b 4. In theillustrated embodiment, each secondary beam distributor 716 is providedas system comprising a beam splitter and a mirror. For example, thefirst secondary beam distributor 716 a includes a beam splitter 718 anda mirror 720. In other embodiments, however, any secondary beamdistributor 716 can be provided as an AOM, one or more polarizers, beamsplitters, spinning chopper mirrors, rotating polygon mirrors,electro-optic modulators (EOMs), or the like or any combination thereof.

The first secondary beam path 116 b 1, second secondary beam path 116 b2, third secondary beam path 116 b 3 and fourth secondary beam path 116b 4 (each generically referred to as a secondary beam path 116 b or,collectively, secondary beam paths 116 b, each propagate to a differentscan head 702. For example, in the illustrated embodiment, the firstprimary optical path 116 a 1 is split by a beam splitter 718 of thefirst secondary beam distributor 716 a to form the first secondary beampath 116 b 1 and the third secondary beam path 116 b 3, and the secondprimary optical path 116 a 2 is split by a beam splitter 718 of thefirst secondary beam distributor 716 b to form the second secondary beampath 116 b 2 and the fourth secondary beam path 116 b 4. The firstsecondary beam path 116 b 1 is directed to the first scan head 702 a,the second secondary beam path 116 b 2 is directed to the second scanhead 702 b, the third secondary beam path 116 b 3 is directed to thethird scan head 702 c and the fourth secondary beam path 116 b 4 isdirected to the fourth scan head 702 d. In the illustrated embodiment,each secondary beam path 116 b serves a set of scan heads 702 on only asingle rail 704. It will be appreciated, however, that any primary beampath 116 a may be split such that its associated secondary beam paths116 b may be delivered to scan heads 702 on different rails 704.

In the illustrated embodiment, optics assemblies, such as first opticsassembly 722 a, second optics assembly 722 b, third optics assembly 722c and fourth optics assembly 722 d (each generically referred to as anoptics assembly 722 or, collectively, optics assemblies 722), aredisposed within the secondary beam paths 116 b, such that an opticsassembly 722 is disposed in a secondary beam path 116 b at a locationupstream of a scan head 702 disposed in the same secondary beam path 116b. Thus, in the illustrated embodiment, the first secondary beam path116 b 1 propagates through first optics assembly 722 a to first scanhead 702 a, the second secondary beam path 116 b 2 propagates throughsecond optics assembly 722 b to second scan head 702 b, the thirdsecondary beam path 116 b 3 propagates through third optics assembly 722c to third scan head 702 c and the fourth secondary beam path 116 b 4propagates through fourth optics assembly 722 d to fourth scan head 702d. It will be appreciated, however, that there may be fewer opticsassemblies 722 than scan heads 702.

Although not shown, an optical bypass system (e.g., comprising one ormore mirrors, AOMs, positioners (e.g., galvanometer mirror systems,fast-steering mirrors, etc.), beam splitters, optical switches, or thelike or any combination thereof) may be disposed in any secondary beampath 116 b to bypass a corresponding optics assembly 722. Thus, when anoptical bypass system is disposed in any particular secondary beam path116 b, an optics assembly 722 can be functionally removed from theparticular secondary beam path 116 b. Alternatively, one or more (orall) of the optics assemblies 722 can be omitted entirely from theapparatus 700.

Each optics assembly 722 can include one or more positioners, such asaforementioned first positioner 106 and, optionally, one or morehalf-wave plates, apertures, relay lenses, mirrors, or the like or anycombination thereof (e.g., all disposed within a common housing havingoptical input and output ports, fixed to a common frame, or the like orany combination thereof). Different optics assemblies 722 can beidentically or differently configured, driven, actuated, or the like orany combination thereof. Thus, a positioner of one optics assembly 722can be of the same or different type as (or be of the same type, buthave a different characteristic as), a positioner of one or more otheroptics assemblies 722. Example characteristics of positioners caninclude the number of positioners (e.g., 1, 2, 3, etc.) of an opticsassembly 722, the type of each positioner of an optical assembly 722,positioning bandwidth, size of scanning range, shape of scanning range,manufacturer, software control, etc. Likewise, a positioner of oneoptics assembly 722 can be driven according to the same controlsignal(s) as a positioner of one or more other optics assemblies 722.Alternatively, a positioner of one optics assembly 722 can be drivenaccording to a different control signal as a positioner of one or moreother optics assemblies 722. Positioners of different optics assemblies722 can be driven simultaneously, sequentially, randomly, or the like orany combination thereof. Each optics assembly 722 can be individuallypackaged as a modular assembly, so it can be selectively removed orreplaced relative to another optics assembly 722.

Although not illustrated, the housing, frame, etc., of one or more ofthe optics assemblies 722 may include a registration feature configuredto facilitate optical alignment of a corresponding secondary beam path116 b within a multi-head apparatus 700 with at least one component ofthe optics assembly 722 (e.g., with a positioner, an aperture, a relaylens, a mirror, an optical input port, an optical output port, or thelike or any combination thereof). Thus, the multi-head apparatus 700 mayfurther include a frame, latch, etc., configured to be engaged with theregistration feature of an optics assembly 722.

As exemplarily shown in FIG. 7, the primary beam distributor 714distributes an incoming train of laser pulses across a set of primarybeam path 116 a (e.g., two primary beam path 116 a), and the secondarybeam distributors 716 distribute incoming trains of laser pulses acrossa set of secondary beam paths 116 b (e.g., four secondary beam paths 116b). In another embodiment, however, one of the secondary beamdistributors 716 disposed along a selected primary beam path 116 a maybe omitted (e.g., along with a corresponding optics assembly 722disposed along a secondary beam path 116 b downstream therefrom), andlaser pulses propagating along the selected primary beam path 116 a maybe directed to a scan head 702 (e.g., with the aid of one or moremirrors, etc.).

Generally, and constructed as described above, one or more components ofthe multi-head apparatus 700 (e.g., the first beam distributor 714, thesecond beam distributors 716, first positioners 106 in the opticsassemblies 722, second positioners 108 in the scan heads 702, etc.) canbe operated (e.g., in response to one or more control signals output bythe controller 114 (see FIG. 1) such that laser pulses (or bursts oflaser pulses) are transmitted from one scan head 702 to the workpiece(not shown) simultaneously with laser pulses (or bursts of laser pulses)from at least one other scan head 702 (or all other scan heads 702) tothe workpiece. In one embodiment, operation of the multi-head apparatus700 is controlled such that laser pulses (or bursts of laser pulses) aredelivered from one scan head 702 supported by a rail 704 simultaneouslywith laser pulses (or bursts of laser pulses) delivered from anotherscan head 702 (or all other scan heads 702) supported by the same rail704. In another embodiment, laser pulses (or bursts of laser pulses) aredelivered from different scan heads 702 supported by a common rail 704(e.g., commonly supported by first rail 704 a or second rail 704 b) at adifferent times.

It will be appreciated that the overall design of the multi-headapparatus 700, including optically desirable distances betweencomponents, may influence the relative positioning of the optionaloptical system 712 and/or its components, the primary beam distributor714, the secondary beam distributors 716, the optics assemblies 722 andtheir components, and the scan heads 702 and/or their components. Anumber of fold mirrors 724 may be employed to facilitate folding thevarious beam paths (e.g., primary beam path 116 a, the secondary beampaths 116 b, etc., each generically referred to as a beam path 116 or,collectively, as beam paths 116) along which laser pulses propagate,e.g., to avoid obstacles, to provide desirable segment lengths, toimprove alignment, or the like or any combination thereof. Some of thesefold mirrors 724, such as first fold mirror 724 a and second fold mirror724 b may be supported by the first rail 704 a and the second rail 704b, respectively. Alternatively or additionally, one or both of the firstfold mirror 724 a and second fold mirror 724 b may be directly orindirectly supported by one or more linear or rotational stages to whicha rail 704 is supported.

Constructed as described above, multiple scan heads 702 of themulti-head apparatus 700 may be used to simultaneously and/orsequentially process multiple, separate workpieces, or may be used tosimultaneously and/or sequentially process a single workpiece. Whenmultiple scan heads 702 are used to process multiple workpieces (e.g.,simultaneously), the apparatus 100 may be provided with multiple thirdpositioners 110, each of which may be operative to move a respectiveworkpiece relative to a scan head. In this case, the third positionersmay be operated to move the workpieces relative to one another, inunison (i.e., so no relative movement between workpieces occurs), or thelike or any combination thereof.

VI. Embodiments Concerning Workpiece Handling System

To facilitate loading or unloading of workpieces into and out of anapparatus such as apparatus 100 or multi-head apparatus 700 (eachgenerically referred to as an apparatus), a workpiece handling system,operative to transfer workpieces onto or off from the third positioner110 (e.g., in response to one or more control signals output by thecontroller 114, by another controller, or the like or any combinationthereof), may be provided.

In one embodiment, and with reference to FIGS. 8 and 9, the workpiecehandling system may be provided as workpiece handling system 800including a storage bay configured to hold one or more workpieces, whichmay be unprocessed by the apparatus, partially processed by theapparatus, fully processed by the apparatus, or any combination thereof.The workpiece handling system 800 can be arranged next to the apparatusto facilitate transfer of workpieces. For example, as shown in FIG. 9,the workpiece handling system 800 can be arranged next to theaforementioned base (e.g., base 802) that supports the third positioner110 (which may optionally, in turn, support a chuck 902). The workpiecehandling system 800 can include a first transfer mechanism 900 operativeto transfer a workpiece 102 from a first handling zone 804 of theworkpiece handling system 800 to the apparatus. The workpiece handlingsystem 800 can also include a second transfer mechanism (not shown)operative to transfer a workpiece 102 to a second handling zone 806 ofthe workpiece handling system 800 from the apparatus. The first transfermechanism 900 and the second transfer mechanism may be provided as arobotic arm (e.g., having an end effector at an end thereof to engagewith the workpiece, etc.), a roll-to-roll handling system such as theROLL MASTER system manufactured by NORTHFIELD AUTOMATION SYSTEMS, or thelike or any combination thereof.

In one embodiment, workpieces to be transferred by the first transfermechanism 900 are pre-aligned in the first handling zone 804 so that,when the first transfer mechanism 900 transfers a workpiece from thefirst handling zone 804 to the apparatus, the workpiece will be disposedat a predetermined location and/or orientation on or over the thirdpositioner 110. In another embodiment, workpieces to be transferred bythe first transfer mechanism 900 are not pre-aligned in the firsthandling zone 804 and, as a result, the first transfer mechanism 900 mayalign the workpiece at a predetermined location and/or orientation on orover the third positioner 110 according to any suitable or beneficialtechnique (e.g., as exemplarily disclosed in aforementioned U.S. Pat.No. 7,834,293).

In one embodiment, the apparatus may be configured to facilitatetransfer of workpieces to and from the workpiece handling system 800.For example, and with reference to FIG. 10, the multi-head apparatus 700may include a third positioner (not shown) configured to move aworkpiece 102 (which may be optionally supported by a chuck 902) withina workpiece movement zone 1000. As shown in FIG. 10, the workpiecemovement zone 1000 encompasses a workpiece loading zone 1002, aworkpiece unloading zone 1004 and a workpiece processing zone 1006. Theworkpiece loading zone 1002 is aligned with the first transfer mechanism900 of the workpiece handling system 800, the workpiece unloading zone1004 is aligned with the second transfer mechanism of the workpiecehandling system 800, and the workpiece processing zone 1006 is alignedwith the scan heads 702 of the multi-head apparatus 700.

Constructed as described above, an example sequence for processingworkpieces using the multi-head apparatus 700 can proceed as follows. Ifthe chuck 902 is not already in the workpiece loading zone 1002, thethird positioner is initially operated to move the chuck 902 into theworkpiece loading zone 1002 and the first robot is operated to transfera workpiece 102 from the first handling zone 804 onto the chuck 902.Next, the third positioner is operated to move the chuck 902, on whichthe transferred workpiece 102 is now supported, (e.g., in the X-,direction, in the Y-direction, or a combination thereof such as alongarrow 1008) from the workpiece loading zone 1002 to the workpieceprocessing zone 1006 (e.g., in alignment with one or more of the scanheads 702). One or more laser pulses are delivered onto the workpiece102 through one or more of the scan heads 702 to process the workpiece102. After processing is complete, the third positioner is operated tomove the chuck 902 (e.g., in the X-, direction, in the Y-direction, or acombination thereof such as along arrow 1010) from the workpieceprocessing zone 1006 into the workpiece unloading zone 1004 and thesecond transfer mechanism is operated to transfer the processedworkpiece 102 from the chuck 902 into the second handling zone 806.Thereafter, the third positioner can be operated to move the chuck 902(e.g., only in the Y-direction such as along arrow 1012) from theworkpiece unloading zone 1004 into the workpiece loading zone 1002 andabove-described sequence may be repeated as necessary.

In one embodiment, the third positioner 110 can be operated to move thechuck 902 faster along one direction than the other. For example, thethird positioner 110 can be operated to move the chuck 902 faster alongthe Y-direction than the X-direction. In one particular embodiment, thethird positioner 110 includes an X-stage and a Y-stage (e.g., providedin a stacked arrangement). The X-stage is configured to impart movementof the chuck along the X-direction at a first speed, and the Y-stage isconfigured to impart movement of the chuck along the Y-direction asecond speed that is greater than the first speed.

As shown in FIG. 10, the workpiece 102 can be conceptually divided intofour regions (e.g., first region I, second region II, third region IIIand fourth region IV) that correspond to the positions of the scan heads702 within the multi-head apparatus 700. Accordingly, when the workpiece102 is disposed within the workpiece processing zone 1006, themulti-head apparatus 700 may be operated to impart relative movementbetween the workpiece 102 and the scan heads 702 from which laser pulsesare delivered during processing (i.e., to impinge upon the workpiece102). As a result, the first region I may be processed by laser pulsesdelivered from the first scan head 702 a, the second region II may beprocessed by laser pulses delivered from the second scan head 702 b, thethird region III may be processed by laser pulses delivered from thethird scan head 702 c and the fourth region IV may be processed by laserpulses delivered from the fourth scan head 702 d. It will beappreciated, that the multi-head apparatus 700 may also be operated toimpart the aforementioned relative movement such that multiple regionsof the workpiece 102 can be processed (e.g., sequentially oralternately) by laser pulses delivered from a common scan head 702.

In one embodiment, the relative positions of the scan heads 702 in themulti-head apparatus 700 may be adjusted as exemplarily described aboveto correspond to dimensions of the particular workpiece 102 to beprocessed, to correspond to dimensions of regions within the particularworkpiece 102 to be processed, or the like or any combination thereof.

Although particular embodiments in this section concerning the workpiecehandling system 800 are discussed in connection with the multi-headapparatus 700, it will be appreciated that any one of these embodiments,or any combination thereof, may be implemented in connection with theapparatus 100 or any other laser-processing apparatus other than theapparatus 100, or any other apparatus (e.g., mechanical drills,water-cutting or drilling apparatus, electron-beam cutting machines,abrasive blasting machines, etc.) beneficially or suitably configured tomachine the workpiece 102.

VII. Embodiments Concerning Scanning Techniques

As used herein, the term “scanning technique” can refer to the manner inwhich a process spot is scanned (e.g., within the first scanning range,the second scanning range, the third scanning range, or the like or anycombination thereof) relative to the workpiece 102, the manner in whichthe first scanning range is scanned within the second scanning range,the manner in which any of the first or second scanning ranges isscanned within the third scanning range, or the like or any combinationthereof. Generally, a scanning technique can be characterized by one ormore parameters such as the process trajectory along which a processspot is to be scanned, direction (i.e., direction along which theprocess spot, first scanning range, second scanning range, or the likeor any combination thereof, is to be scanned), scan rate (i.e., speedwith which the process spot, first scanning range, second scanningrange, or the like or any combination thereof, is to be scanned), or thelike or any combination thereof.

A. Facilitating Z-Height Measurement, Compensation, etc.

In the embodiments discussed in this section, the apparatus 100 includesa Z-height sensor, such as Z-height sensor 124, which is positionallyfixed relative to the scan lens 112. As a result, whenever relativemovement between the second scanning range 302 b and the workpiece 102is imparted (i.e., whenever the second scanning range is “scanned,”which may be accomplished by operating the third positioner 110), thesensing range 402 is also scanned in unison (e.g., in the same directionand at the same speed) with the second scanning range 302 b. The secondscanning range 302 b (and, thus, the sensing range 402) can be scannedat a scan rate in a range from 25 mm/sec to 200 mm/sec. In oneembodiment, the scan rate is in a range from 50 mm to 100 mm/sec.Depending upon factors such as processing speed, speed and/or accuracywith which Z-height measurements can be made, variation in surfacetopology of the worksurface 102 a, etc., the scan rate can be less than25 mm/sec or greater 200 mm/sec.

As mentioned above, offsetting the sensing range 402 relative to thesecond scanning range 320 b as discussed above with respect to FIGS. 4to 6 can lead to certain problems during processing of the workpiece102. However these problems (or susceptibility to problems) can beameliorated or avoided by raster-scanning the second scanning range 302b (and, thus, the sensing range 402) along a process trajectory defininga scan pattern that includes a plurality of strips or segments (e.g.,which may be straight, curved, or a combination thereof) which areparallel or non-parallel with each other. Raster scanning may beperformed according to a unidirectional scanning technique, abidirectional raster-scanning technique, or the like or any combinationthereof, examples of each of which are described in greater detailbelow. It will be appreciated that the scanning range 302 b (and, thus,the sensing range 402) may be vector-scanned, arranged according to astep-and-repeat technique, or the like or any combination thereof, inaddition to (or as an alternative to) being raster-scanned.

For purposes of facilitating discussion of the raster-scanningtechniques discussed herein, each portion of a workpiece that coincideswith a segment of a raster-scan pattern will also be referred to hereinas a “segment” of the workpiece or, more simply, a “workpiece segment.”Generally, each workpiece segment includes a portion of the workpiecethat is to be processed by the apparatus 100 (e.g., to form one or moreor features, etc.). In one embodiment however, at least one workpiecesegment does not include any portion of the workpiece that is to beprocessed by the apparatus 100.

Any two workpiece segments may overlap one another, adjoin one another,or be spaced apart from one another. As used herein, two parallelworkpiece segments are considered to be “adjacent” to one another ifthere is no intervening workpiece segment (either parallel ornon-parallel) therebetween. Thus, two workpiece segments can be adjacentif they adjoin or are spaced apart from one another. In embodiments inwhich multiple pairs of parallel, spaced-apart workpiece segments exist,the distances between workpiece segments of at least two pairs ofworkpiece segments may be the same or different. Further, the distancebetween any pair of adjacent workpiece segments may be set manually(e.g., by the user) or automatically (e.g., at the controller 114), orthe like or a combination thereof. When set automatically, the distancebetween any pair of adjacent workpiece segments may be set according tothe length (or width) of the second scanning range 302 b (e.g., asmeasured along a direction that is perpendicular to the scan direction),according to the placement of the sensing range 402 relative to thesecond scanning range 302 b, according to the size and/or shape of thesensing range 402, according to optimization of a cost functionrepresenting, for example, the total amount of time necessary to processall of the workpiece segments), or the like or any combination thereof.

As used herein, the direction in which the second scanning range 302 bis raster-scanned while laser pulses are delivered to the workpiece(thus forming a process spot) is referred to as the “scan direction.”Likewise, the scan direction also refers to the direction in which thesensing range 402 is scanned while Z-height measurements are obtained.In the embodiments described below, the width of a workpiece segment(e.g., as measured along a direction that is perpendicular to the scandirection) is equal to the length (or width) of the second scanningrange 302 b (e.g., as measured along a direction that is perpendicularto the scan direction). In another embodiment, however, the width of aworkpiece segment is less than, or greater than, the length (or width)of the second scanning range 302 b (e.g., as measured along a directionthat is perpendicular to the scan direction). Also in the embodimentsdescribed below, all workpiece segments of the same workpiece may havethe same width (e.g., as measured along a direction that isperpendicular to the scan direction). In other embodiments, at least twoof the workpiece segments may have different widths (e.g., wherein atleast of the widths is less than, equal to, or greater than a length (orwidth) of the second scanning range 302 b, as measured along a directionthat is perpendicular to the scan direction). Further, the width of anyworkpiece segment may be set manually (e.g., by the user), automatically(e.g., at the controller 114), or the like or a combination thereof.When set automatically, the width of a workpiece segment may be setaccording to the length (or width) of the second scanning range 302 b(e.g., as measured along a direction that is perpendicular to the scandirection), according to the placement of the sensing range 402 relativeto the second scanning range 302 b, according to the size and/or shapeof the sensing range 402, according to optimization of a cost functionrepresenting, for example, the total amount of time necessary to processall of the workpiece segments), or the like or any combination thereof.

Although particular embodiments concerning certain scanning techniques,Z-height measurements, Z-height compensation, etc., are discussed inthis section in connection with apparatus 100, it will be appreciatedthat any one of these embodiments or any combination thereof, may beimplemented in connection with the multi-head apparatus 700. It will befurther appreciated that the embodiments discussed in this section maybe implemented with any suitably-equipped single- or multi-headlaser-processing apparatus other than those discussed herein, or anyother apparatus (e.g., mechanical drill, water-cutting or drillingapparatus, electron-beam cutting machines, abrasive blasting machines,etc.) beneficially or suitably configured to machine the workpiece 102.

i. Unidirectional Scanning

According to a unidirectional raster-scanning technique, the sensingrange 402 and the second scanning range 302 b are sequentially scannedalong a common workpiece segment in a single scan direction. The sensingrange 402 and the second scanning range 302 b are also scanned alongadjacent workpiece segments in a single scan direction.

To facilitate unidirectional raster-scanning, the apparatus 100 mayinclude a Z-height sensor arranged and configured to project a sensingrange 402 that is offset from the second scanning range 302 b in adirection that is the same as the scan direction. For example, and withreference to FIG. 4 or 6, if the scan direction is the −Y-direction,then the sensing range 402 may also be offset from the second scanningrange 302 b in the −Y-direction. In another example, and with referenceto FIG. 5 or 6, if the scan direction is the −X-direction, then thesensing range 402 may also be offset from the second scanning range 302b in the −X-direction.

Prior to processing, the relative position between the workpiece and thesensing range 402 is initially set such that the sensing range 402 isaligned at or near an end of the workpiece segment of the workpiece tobe processed. For example, as illustrated in FIG. 11, the sensing range402 (offset from the second scanning range as discussed with respect toFIG. 4) is aligned at an end of a current workpiece segment 1102 to beprocessed. Likewise, as illustrated in FIG. 15, the sensing range 402(offset from the second scanning range as discussed with respect to FIG.5) is aligned at an end of a current workpiece segment 1502 to beprocessed.

After the sensing range 402 is aligned with the current workpiecesegment, the second scanning range 302 b and sensing range 402 arescanned, in unison, along the segment in a scanning direction (e.g., inthe −Y- or −X-directions, as shown in FIGS. 12 and 16, respectively).Accordingly, the sensing range 402 is scanned along the currentworkpiece segment to be processed, ahead of the second scanning range302 b. During scanning of the sensing range 402, Z-height measurementsat various sensing positions are obtained and optionally stored (and,further optionally, processed as discussed above).

During scanning of the second scanning range 302 b, laser pulses may bedelivered to the portions of the current workpiece segment to beprocessed. If worksurface Z-height (e.g., either as previously measuredor processed, and stored) at a particular sensing position is determinedto be outside the predetermined nominal Z-height process window, thenZ-height compensation can be effected (e.g., as discussed above) whenthe processing position is the same as (or is within a specifieddistance of) the particular sensing position.

After processing the current workpiece segment (e.g., when the secondscanning range 302 b is at or near the end of the current workpiecesegment, as shown in FIG. 13 or 17), the relative position between theworkpiece and the sensing range 402 is indexed such that the sensingrange 402 is aligned at or near an end of a next workpiece segment to beprocessed (e.g., segment 1104 or segment 1504, as shown in FIGS. 14 and18, respectively) and the above-described process may be repeated.

ii. Bidirectional Scanning

According to a bidirectional raster-scanning technique, the sensingrange 402 and the second scanning range 302 b are sequentially scannedalong a common workpiece segment in opposite scan directions. Each ofthe sensing range 402 and the second scanning range 302 b are alsoscanned along adjacent workpiece segments in opposite scan directions.

To facilitate bidirectional raster-scanning, the apparatus 100 mayinclude a Z-height sensor arranged and configured to project a sensingrange 402 that is offset from the second scanning range 302 b in adirection that is different from the scan direction. For example, andwith reference to FIG. 4 or 6, if the scan direction is the +X or−X-direction, then the sensing range 402 may be offset from the secondscanning range 302 b in the +Y- or −Y-direction. In another example, andwith reference to FIG. 5 or 6, if the scan direction is the +Y- or−Y-direction, then the sensing range 402 may be offset from the secondscanning range 302 b in the +X or −X-direction.

Prior to processing, the relative position between the workpiece and thesensing range 402 is initially set such that the sensing range 402 isaligned at or near an end of a workpiece segment to be processed. Forexample, as illustrated in FIG. 19, the sensing range 402 (offset fromthe second scanning range as discussed with respect to FIG. 5) isaligned at an end of aforementioned workpiece segment 1100 a 1.Likewise, as illustrated in FIG. 22, the sensing range 402 (offset fromthe second scanning range as discussed with respect to FIG. 4) isaligned at an end of aforementioned workpiece segment 1502.

After the sensing range 402 is aligned with a workpiece segment to beprocessed, the second scanning range 302 b and sensing range 402 arescanned, in unison, such that the sensing range 402 is scanned in afirst scanning direction (e.g., in the −Y- or −X-direction as shown bythe arrow in FIG. 20 or 23, respectively) along the workpiece segment tobe processed (e.g., segment 1100 a 1 or segment 1502, as shown in FIGS.21 and 24, respectively). During scanning of the sensing range 402 inthe first scanning direction, Z-height measurements at various sensingpositions along the workpiece segment are obtained and optionally stored(and, further optionally, processed as discussed above).

After measuring a workpiece segment to be processed with the Z-heightsensor 124 (e.g., when the sensing range 402 is at or near an end of theworkpiece segment 1100 a 1 or 1502 to be processed, as shown in FIG. 20or 23), the relative position between the workpiece and the sensingrange 402 is indexed such that the sensing range 402 is aligned at ornear an end of another workpiece segment to be processed (e.g., segment1104 or segment 1504, as shown in FIGS. 21 and 24, respectively). Since,in the embodiments discussed herein, the Z-height sensor 124 ispositionally fixed relative to the scan lens 112, the second scanningrange 302 b also becomes aligned at or near an end of a workpiecesegment that was previously measured by the Z-height sensor 124 (e.g.,previously-measured segment 1100 a 1 or segment 1502, as shown in FIGS.21 and 24, respectively).

After indexing the sensing range 402 and second scanning range 302 b asdiscussed above, the second scanning range 302 b and sensing range 402are scanned, in unison, in a second scanning direction opposite thefirst scanning direction (e.g., in the +Y- or +X-direction as shown bythe arrows in FIG. 21 or 24, respectively). As a result, the sensingrange 402 is scanned along another workpiece segment to be processed(e.g., along segment 1104 or segment 1504, as shown in FIGS. 21 and 24,respectively) while the second scanning range 302 b is scanned along apreviously-measured workpiece segment (i.e., along segment 1100 a 1 orsegment 1502, as shown in FIGS. 21 and 24, respectively).

During scanning of the sensing range 402 in the second scanningdirection, Z-height measurements at various sensing positions areobtained and optionally stored (and, further optionally, processed asdiscussed above). During scanning of the second scanning range 302 b inthe second scanning direction, laser pulses may be delivered to portionsof the previously-measured workpiece segment (i.e., segment 1100 a 1 orsegment 1502, as shown in FIGS. 21 and 24, respectively). If theworksurface Z-height (e.g., either as measured or processed) at aparticular sensing position is determined to be outside thepredetermined nominal Z-height process window, then Z-heightcompensation can be effected (e.g., as discussed above) when theprocessing position is the same as (or is within a specified distanceof) the particular sensing position.

After a previously-measured workpiece segment (e.g., workpiece segment1100 a 1 or 1502) has been processed and another (e.g., unprocessed)workpiece segment (e.g., workpiece segment 1104 or 1504) has beenmeasured, indexing may again be performed to align the sensing range 402at or near an end of another workpiece segment (not shown) to bemeasured and to align the second scanning range 302 b at or near the endof a previously-measured workpiece segment (e.g., segment 1104 orsegment 1504). After alignment, the sensing range 402 and the secondscanning range 302 b are scanned, in unison, in the first scanningdirection as and the above-described processes involving measuring,processing, Z-height compensation, etc., may be repeated.

B. Facilitating Feature Formation

As mentioned above, the first positioner 106 has a first positioningbandwidth in a range from 50 kHz to 10 MHz, and thus can be used torapidly scan the process spot within the first scanning range to formone or more features (e.g., one or more openings, vias, trenches, slots,scribe lines, recessed regions, etc.) in the workpiece 102. As alsomentioned above, the maximum dimension of the feature to be formed inthe workpiece 102 (e.g., as measured in the X-Y plane) may be less thanor equal to the maximum dimension first scanning range (e.g., in the X-or Y-directions). In another embodiment however, the maximum dimensionof the feature may be greater than the maximum dimension of the firstscanning range.

Generally, the first positioner 106 can be operated to scan the processspot along the X-direction (e.g., in the +X or −X direction) and/oralong the Y-direction (e.g., in the +Y or −Y direction) while the secondpositioner 108 scans the first scanning range along the X-direction(e.g., in the +X or −X direction), while the second positioner 108 scansthe first scanning range along the Y-direction (e.g., in the +Y or −Ydirection), while the third positioner 110 scans the first and/or secondscanning ranges along the X-direction (e.g., in the +X or −X direction),while the third positioner 110 scans the first and/or second scanningranges along the Y-direction (e.g., in the +Y or −Y direction), or anycombination thereof. Nevertheless, it should be recognized that thefirst positioner 106 can be operated to scan the process spot along theX-direction (e.g., in the +X or −X direction) and/or along theY-direction (e.g., in the +Y or −Y direction) when the second positioner108 is not scanning the first scanning range, when the third positioner110 is not scanning the first or second scanning ranges, or anycombination thereof. It should also be recognized that, at any point intime, the direction along which (or in which) the process spot isscanned by the first positioner 106 can the same as, or different from,the direction along which (or in which) the first scanning range isscanned within the second scanning range by the second positioner 108,the direction along which (or in which) the first scanning range isscanned within the third scanning range by the third positioner 110, orany combination thereof.

In some embodiments, the workpiece 102 is provided as a PCB panel, aPCB, an FPC, an IC, an ICP, a semiconductor device, etc. Thus, theworkpiece 102 may include one or more constituent structures such as anelectrical conductor structure (e.g., such as a film, foil, etc., whichmay be formed of copper, a copper alloy, an interconnect or wiringstructure comprising one or more metals such as copper, titanium,titanium nitride, tantalum, etc., or the like or any combinationthereof), a dielectric structure (e.g., a build-up film, aglass-reinforced epoxy laminate, an interlayer dielectric material, alow-k dielectric material, solder resist, or the like or any combinationthereof. When provided as a PCB panel or PCB, the workpiece 102 mayinclude a dielectric structure (e.g., a glass-reinforced epoxy laminate)adhered to a first conductor (e.g., a copper or copper alloy foil, whichmay have an exposed surface that is either darkened—e.g., by a chemicalreaction, by a laser-darkening process, etc.—or that is not darkened) ata first side thereof and, optionally, to a second conductor (e.g., apad, a trace, foil, etc., formed of copper or a copper alloy) at asecond side thereof that is opposite the first side. One or morefeatures (e.g., one or more openings, slots, grooves, blind vias,through vias, slot vias, etc.) may be formed in or on one or morecomponents of the workpiece 102 by removing material therefrom (e.g., asduring a cutting process, a drilling process, an engraving process, arouting process, or the like or any combination thereof) due to ablationof the material. As used herein, the term “feature region” refers to aregion of a workpiece 102 that is to be processed to form a feature.

Generally, and unless explicitly stated otherwise, the term “ablation”can refer to “direct ablation,” “indirect ablation” or any combinationthereof. Direct ablation of a material in the workpiece 102 occurs whenthe dominant cause of ablation is decomposition of the material due toabsorption (e.g., linear absorption, nonlinear absorption, or anycombination thereof) of energy within the beam of delivered laser energyby the material. Indirect ablation (also known as “lift-off”) of amaterial in the workpiece 102 occurs when the dominant cause of ablationis melting and vaporization due to heat generated in, and transportedfrom, an adjacent material which absorbs the energy within the beam ofdelivered laser energy.

In one embodiment, the feature may be formed to extend, completely orpartially, through one or more components of the workpiece 102 (e.g.,one or more electrical conductor structures, one or more dielectricstructures, or the like or any combination thereof). In one embodiment,the electrical conductor structure or dielectric structure can have athickness in a range from 5 μm to 500 μm. It will be appreciated,however, that an electrical conductor structure or a dielectricstructure can have a thickness smaller than 5 μm or larger than 500 μm.Thus, a thickness of an electrical conductor structure or dielectricstructure can be greater than or equal to 1 μm, 3 μm, 5 μm, 10 μm, 15μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 50 μm, 70 μm, 80 μm, 100μm, 110 μm, 120 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 550 μm, 600μm, etc., or between any of these values. Likewise, the thickness can beless than 550 μm, 450 μm, 400 μm, 350 μm, 300 μm, 250 μm, 120 μm, 110μm, 100 μm, 80 μm, 70 μm, 50 μm, 40 μm, 35 μm, 25 μm, 20 μm, 18 μm, 15μm, 10 μm, 5 μm, 3 μm, 1 μm, 0.5 μm, 0.1 μm, etc., or between any ofthese values.

Generally, the top portion of the feature may have a diameter (i.e., a“top diameter”) in a range from 5 μm to 300 μm. It will be appreciated,however, that the top diameter can be smaller than 5 μm or larger than300 μm. Thus, the top diameter may be greater than or equal to 5 μm, 10μm, 20 μm, 30 μm, 40 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 200 μm,250 μm, 150 μm, 200 μm, 250 μm, 300 μm, 320 μm, etc., or between any ofthese values. Likewise, the top diameter can be less than 350 μm, 300μm, 250 μm, 200 μm, 150 μm, 120 μm, 100 μm, 80 μm, 50 μm, 40 μm, 30 μm,20 μm, 10 μm, 5 μm, etc., or between any of these values.

Generally, the bottom portion of the feature may have a diameter (i.e.,a “bottom diameter”) that is less than or equal to the top diameter. Thedifference between the top and bottom diameters is herein referred to asthe “taper” of the feature, or simply the “feature taper.” Feature taperis indicative of the slope of a sidewall of the feature within theworkpiece 102. Often it is desirable to form features having arelatively small taper (e.g., to facilitate formation of a large numberof features within a relatively small region of the workpiece 102). Ifthe feature is a via, then a relatively small taper can facilitatereliable plating or filling thereof. One factor affecting taper is thedepth of the feature that is formed; features with relatively smalldepths tend to have either zero taper, or smaller tapers than featureswith relatively large depths. In the present example, the taper of afeature formed in the workpiece 102 can be less than or equal to 20 μm.For example, the taper can be less than or equal to 18 μm, 15 μm, 12 μm,10 μm, 9 μm, 8 μm, 7.5 μm, 7 μm, 6 μm, 5 μm, 4 μm, 3 μm, 2 μm, 1 μm, 0.5μm, etc., or between any of these values.

Generally, the depth of the feature is measured along an axis (alsoreferred to herein as a “feature axis”) that extends through the top andbottom portions of the feature. In one embodiment, the depth of thefeature corresponds to the thickness of the one or more structures inwhich it is formed (in which case, the feature extends completelythrough one or more structures). In another embodiment, the depth of thefeature does not correspond to the thickness of the structure in whichit is formed (in which case, the feature extends only partially througha structure). Thus, the feature may have a depth in a range from 5 μm to250 μm (or smaller than 5 μm or larger than 250 μm). For example, thefeature may have a depth greater than or equal to 1 μm, 3 μm, 5 μm, 10μm, 15 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 50 μm, 70 μm, 80μm, 100 μm, 110 μm, 120 μm, 250 μm, 300 μm, etc., or between any ofthese values. Likewise, the depth can be less than 300 μm, 250 μm, 120μm, 110 μm, 100 μm, 80 μm, 70 μm, 50 μm, 40 μm, 35 μm, 25 μm, 20 μm, 18μm, 15 μm, 10 μm, 5 μm, 3 μm, 1 μm, 0.5 μm, 0.1 μm, etc., or between anyof these values.

Generally, feature formation may be performed by scanning a process spotalong a process trajectory that defines one or more scan patterns (e.g.,by controlling the first positioner 106 to scan a process spot accordingto one or more corresponding scan patterns within the first scanningrange). Depending upon one or more factors such as the desired depth ofthe feature to be formed, the material(s) to be removed during featureformation, one or more parameters of the beam of laser pulses to bedelivered during feature formation, or the like or any combinationthereof, the feature may be formed by scanning a process spot along ascan pattern (also referred to as a “feature-forming” scan pattern) onlyonce, or multiple times. When a process spot is scanned along a scanpattern multiple times, scanned along a scan pattern multiple times, theprocess spot can be repeatedly scanned along the same scan pattern(i.e., the same scan pattern can be repeatedly used). In anotherembodiment, at least two different scan patterns can be used duringfeature formation. In the event that the same scan pattern is repeatedlyused, a subsequently-used scan pattern can have the same orientation(e.g., measured relative to the feature axis) as, or a differentorientation from, the orientation of a previously-used scan pattern.

Although particular embodiments concerning certain scanning techniquesare discussed in this section in connection with apparatus 100, it willbe appreciated that any of these embodiments or any combination thereof,may be implemented in connection with the multi-head apparatus 700. Itwill be further appreciated that the embodiments discussed in thissection may be implemented with any suitably-equipped single- ormulti-head laser-processing apparatus other than those discussed herein,or any other suitable apparatus (e.g., mechanical drill, water-cuttingor drilling apparatus, electron-beam cutting machines, abrasive blastingmachines, etc.) beneficially or suitably configured to process theworkpiece 102.

i. Example Embodiments of Scan Patterns

Examples of scan patterns for forming features such as vias or otherholes, openings, recesses, trenches, etc., include scan patterns 2500,2600, 2700 and 2800, shown in FIGS. 25, 26, 27 and 28, respectively, orthe like or any combination thereof. Generally, the scan pattern mayresemble or otherwise delineate a raster pattern (e.g., as illustratedin FIG. 25), a star polygon or a star-shaped polygon (e.g., asillustrated in FIG. 26), a spiral or a set of arcs or circles(concentrically arranged or otherwise, e.g., as illustrated in FIG. 27),a circle (e.g., as illustrated in FIG. 28), a set of circles, or one ormore shapes (e.g., ellipses, triangles, squares, rectangles, or otherregular or irregular shapes, etc.), or the like or any combinationthereof. In one embodiment, one or more scan patterns (e.g., one or morescan patterns 2500, 2600, 2700 or 2800, or any combination thereof) maybe used to remove material (e.g., by direct ablation, indirect ablation,or any combination thereof) from one or more electrical conductorstructures, one or more dielectric structures, or the like or anycombination thereof, during formation of a feature such as a circularopening, a via, etc.

In FIGS. 25 to 28, the dashed line 2502 represents the desired boundary,at the worksurface 102 a, for a feature (e.g., a circular opening orvia, in the present example) to be formed an electrical conductorstructure or dielectric structure of the workpiece 102. For purposes ofdiscussion with the present example, once formed in the workpiece 102,the feature can be characterized as including a “top portion” formed atthe worksurface 102 a and extending along an axis into the workpiece 102(e.g., to either terminate within the workpiece 102, or extendcompletely through the workpiece 102). The portion of the feature thusterminating within the workpiece 102 or present at the other side of theworkpiece 102 may herein be referred to as a “bottom portion” of thefeature.

Although FIGS. 25 to 28 illustrate the boundary 2502 of the feature tobe formed (also referred to herein as a “feature boundary”) as beingcircular, it will be appreciated that the boundary may have any suitableor desired shape (e.g., elliptical, square, rectangular, triangular,hexagonal, irregular, or the like or any combination thereof. In theembodiments discussed herein, the shape of the boundary 2502 at the topand bottom portions of the feature is the same or similar (e.g.,circular). In other embodiments (e.g., in which removal of a materialoccurs by direct ablation, and multiple scan patterns are scanned duringprocessing of the material), the boundary 2502 at the top portion of thefeature may be different from the shape of the boundary 2502 at thebottom portion of the feature. For example, the top portion of thefeature may have a boundary 2502 that is circular while the top portionof the feature may have a boundary 2502 that is elliptical, rectangular,etc.).

The centers of locations for process spots within a scan pattern (eachgenerically referred to as a “spot location” or, collectively, “spotlocations”) are indicated by diamonds 2504. Although scan patterns 2500,2600, 2700 and 2800 are illustrated as having the particular arrangementof spot locations 2504 shown, it will be appreciated that any scanpattern may include more or fewer spot locations, in any suitable ordesired arrangement. The arrangement of spot locations 2504 (i.e., whichcan be characterized by the number of spot locations, the positions ofthe spot locations, the pitch between adjacent spot locations, or thelike or any combination thereof), within a scan pattern or disposedalong a common scan line, can vary depending upon factors such as thethermal conductivity, thermal diffusivity, specific heat capacity,optical absorptivity, etc., of material at or near the spot location,the viscosity of material at or near the spot location during theformation of the feature, the optical absorptivity (relative to the beamof delivered laser energy) of material at or near the spot location, thepresence or absence of any electrical conductor or dielectric structuresnear the spot location, the geometrical configuration of any electricalconductor or dielectric structures near the spot location, the spotsize, type and shape of spatial intensity profile, pulse duration,fluence, pulse repetition rate, scan rate, the size and shape of thefeature to be formed, or the like or any combination thereof. Generally,the arrangement of spot locations commonly disposed along one scan lineof a particular scan pattern can be the same as, or different from, thearrangement of spot locations commonly disposed along another scan lineof the particular scan pattern.

Among the spot locations 2504, spot location 2504 a represents the firstspot location in the scan pattern to be irradiated with a laser pulseand spot location 2504 b represents the last spot in the scan pattern tobe irradiated with a laser pulse. Accordingly, the solid line connectingthe spot locations 2504 indicates the sequence in which the spotlocations 2504 are addressed (e.g., by one or more delivered laserpulses). It should be recognized, however, that spot locations 2504within a scan pattern may be addressed in any other desired sequence(thus changing the configuration of the solid line), and may even beaddressed randomly. At any time during processing, a spot location 2540in a scan pattern can be characterized as a previously-addressed spotlocation (i.e., a spot location to which laser pulses were delivered), acurrently-addressed spot location (i.e., a spot location to which laserpulses are being delivered) and a to-be-addressed spot location (i.e., aspot location to which laser pulses will be delivered).

In one embodiment, the arrangement of spot locations 2504 and thesequence with which spot locations 2504 are addressed is, optionally,selected to reduce or avoid undesirable accumulation of heat (e.g.,which can result in undesirable cracking, melting, vaporization,ablation, crystallization, annealing, carbonization, oxidation, etc.)within the workpiece 102 during feature formation. In another embodiment(and as described in greater detail below), the arrangement of spotlocations 2504 and the sequence with which spot locations 2504 areaddressed is, optionally, selected to affect (e.g., reduce) the taper ofa feature that is ultimately formed. In another embodiment, thearrangement of spot locations 2504 and the sequence with which spotlocations 2504 are addressed is, optionally, selected to promote heatingof the workpiece 102 in a manner that facilitates efficient formation ofone or more features on or within the workpiece 102.

Depending upon one or more factors such as pulse repetition rate, thefirst positioning bandwidth, the scan pattern to be scanned, etc., atleast two temporally-sequential laser pulses (e.g., 2 laser pulses, 3,laser pulses, 5 laser pulses, 8 laser pulses, 10 laser pulses, 20 laserpulses, etc.) may be delivered to the same spot location 2504, or todifferent spot locations 2504. In this case, the pulse repetition ratecan be generally characterized as being greater than the firstpositioning bandwidth. In another embodiment, however, the pulserepetition rate can be less than or equal to the first positioningbandwidth. The period of time during which temporally-sequential laserpulses are delivered to the same spot location 2504 (or otherwisedelivered within a local vicinity of a common spot location 2504) isherein referred to as a “dwell time” associated with that spot location2504. For purposes of discussion, a laser pulse is considered to bedelivered to a local vicinity of a spot location 2504 if it is deliveredto within 1 μm of the spot location 2504. In one embodiment, a laserpulse is considered to be delivered to a local vicinity of a spotlocation 2504 if it is delivered to within 10.0 μm, 8.0 μm, 7.0 μm, 6.0μm, 5.0 μm, 4.0 μm, 3.5 μm, 3.0 μm, 2.5 μm, 2.0 μm, 1.5 μm, 1.0 μm, 0.9μm, 0.8 μm, 0.75 μm, 0.7 μm, 0.65 μm, 0.6 μm, 0.5 μm, 0.4 μm, 0.3 μm,0.25 μm, 0.2 μm, 0.15 μm, 0.1 μm, 0.08 μm, 0.05 μm, 0.01 μm, or lessthan 0.01 μm, of the spot location 2504.

In the illustrated embodiments, a scan pattern can be characterized asincluding one or more series of sequentially-addressed spot locations2504. Each such series of spot locations 2504 can generally becharacterized as being disposed along a common scan line. Generally,sequentially-addressed spot locations disposed on a common scan line arecloser to one another than sequentially-addressed spot locationsdisposed on different scan lines. A scan line may be straight (e.g., asillustrated in FIG. 25 or 26), curved (e.g., as illustrated in FIG. 27or 28), or the like or any combination thereof. For example, the scanpattern 2500 shown in FIG. 25 includes a plurality of straight, parallelscan lines whereas the scan pattern 2600 shown in FIG. 26 includes aplurality of straight scan lines that are oblique relative to oneanother. The scan lines in scan pattern 2600 extend along axes which, inturn, extend radially (or generally radially) from a center of thefeature boundary 2502 (or from a central region encompassing the centerof the feature boundary 2502) toward the feature boundary 2502. The scanpattern 2700 shown in FIG. 27 includes a plurality ofconcentrically-arranged arcuate scan lines (the radially-outermost oneof which extends along the desired feature boundary 2502). The scanpattern 2800 shown in FIG. 28 includes a single arcuate scan line (e.g.,extending along the desired feature boundary 2502).

At least one laser pulse is delivered to each spot location 2504. In oneembodiment, multiple laser pulses are delivered to one or more spotlocations 2504 (or otherwise delivered within a local vicinity of acommon spot location 2504). Generally, the same number of laser pulsesare delivered to at least two spot locations 2504 of a scan pattern, ordifferent numbers of laser pulses can be delivered to at least two spotlocations 2504 of a scan pattern.

Generally, the pitch between adjacent spot locations 2504 is consideredto be greater than the distance encompassed within the local vicinity ofa spot location 2504. In one embodiment, a pitch between adjacent spotlocations within a scan pattern can be in a range from 0.1 μm to 50 μm.Likewise, a pitch between adjacent spot locations 2504 disposed along acommon scan line may be in a range from 0.1 μm to 50 μm. Thus, a pitchbetween adjacent spot locations 2504 (either within the scan pattern,generally, or disposed along a common scan line) may be greater than orequal to 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 3μm, 3.5 μm, 4.5 μm, 5 μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, 55 μm, 60μm, 80 μm, etc., or between any of these values, or less than 50 μm, 40μm, 30 μm, 20 μm, 15 μm, 10 μm, 5 μm, 4.5 μm, 3.5 μm, 3 μm, 2 μm, 1.5μm, 1 μm, 0.5 μm, 0.4 μm, 0.3 μm, 0.2 μm, 0.1 μm, 0.08 μm, 0.05 μm, 0.01μm, etc., or between any of these values. For purposes of discussionherein, the pitch between spot locations is measured as the distancebetween the centers of two adjacent spot locations. Two spot locationsare considered to be adjacent to one another if no intervening spotlocation exists therebetween.

Among pairs of adjacent spot locations 2504 (either within the scanpattern, generally, or disposed along a common scan line), the pitchtherebetween can be constant, variable, or any combination thereof. Inone embodiment, the pitch between adjacent spot locations disposed alonga common scan line can increase or decrease in a direction extendingfrom a spot location where one laser pulse is delivered and another spotlocation where a laser pulse is subsequently delivered. Thus, the pitchbetween adjacent spot locations disposed along a common scan line can beconstant, can increase, or can decrease, or any combination thereof,while moving along the scan line. Generally, the spot size of thedelivered laser pulses, and the pitch between pairs of adjacent spotlocations 2504, can be selected or otherwise set such that spot areasirradiated by laser pulses delivered to the pair of adjacent spotlocations 2504 overlap one another, or do not overlap one another.

In one embodiment, the arrangement of scan lines (i.e., which can becharacterized by the number of scan lines, the orientation of a scanline relative to another scan line, the orientation of a scan linerelative to the boundary 2502, the length of a scan line, the pitchbetween adjacent scan lines, etc.) within the scan pattern is notlimited to the arrangements shown in FIGS. 25 to 28, and can varydepending upon one or more factors such as those described above withrespect to the arrangement of spot locations 2504. Thus, a scan patterncan have an odd number of scan lines or an even number of scan lines. Inone embodiment, the number of scan lines in a scan pattern can be in arange from 1 to 64. For example, the number of scan lines in a scanpattern be greater than or equal to 2, 4, 8, 16, 32, 50, 60, etc., orless than 64, 32, 16, 8, 4, 2. It should also be recognized that scanpattern can have more than 64 scan lines. Within a scan pattern, atleast some of the scan lines can be arranged symmetrically (or at leastsubstantially symmetrically) or be arranged asymmetrically. Examples ofsymmetrical arrangements include rotationally symmetrical arrangements(i.e., n-fold rotational symmetry, where n is any integer greater than1, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 50, etc.) andreflective symmetrical arrangements.

ii. Considerations Regarding Anisotropic Material Removal

a. Theory

Through experiments and multi-physics modeling, the inventors directedlaser pulses along a beam axis that was scanned (with minimal or nochange in angle of incidence of the beam axis at the worksurface 102 a)along a scan line (e.g., extending in the +X-direction, as shown in FIG.29), and delivered such laser pulses to directly ablate a workpiece 102(e.g., a dielectric structure such as ABF, solder resist,glass-reinforced epoxy laminate, etc.) to form a plurality of trenchestherein, such as trench 2900 which is schematically shown in FIGS. 29,29A and 29B. In FIG. 29, the scan line along which the beam of laserpulses is scanned includes a plurality of spot locations (i.e., “n” spotlocations, where n is 2, 3, 4, 5, etc.), and the spot area irradiated byone or more laser pulses delivered to the first spot location is denotedat 2906 a, the spot area irradiated by one or more laser pulsesdelivered to the second spot location is denoted at 2906 b, etc., andthe spot area irradiated by one or more laser pulses delivered to thefinal spot location (also referred to herein as a “terminal spotlocation”) is denoted at 2906 n. During experiments, trenches having alength in a range from a few tens of μm to a few millimeters wereformed. FIGS. 29A and 29B are cross-sectional views of the trench shownin FIG. 29, taken along lines XXIXA-XXIXA and XXIXB-XXIXB′,respectively, shown in FIG. 29. As used herein the scan line along whichthese spot locations are disposed is referred to as an “anisotropicmaterial removal scan line.” When formed as discussed above, theterminal end 2902 of the trench 2900 was discovered to have less taperthan the beginning end 2904 of the trench 2900 (see FIG. 29B) when thelaser pulses were delivered at a sufficiently high pulse repetitionrate, and were characterized by other parameters such as spot size,average power, etc., sufficient to directly ablate the workpiece 102).Thus the trench-formation process described above appears to exhibitanisotropic material removal properties. While not necessarily wishingto be bound by any particular theory, simulations appear to indicatethat this anisotropic material removal phenomenon is (at least partly)attributable to at least one of two factors.

One of the aforementioned factors relates to the temperature of a regionof the workpiece 102 before it is irradiated with laser pulses.Initially, the workpiece 102 is relatively cool when a first spotlocation along the scan line is irradiated with laser pulses and, as aresult, a material removal mechanism at the first spot location isrelatively inefficient. Consequently, after a number of laser pulseshave been delivered, the taper of the resultant sidewall formed in theworkpiece 102 at the first spot location is relatively large. After afew laser pulses have been delivered, however, heat begins to accumulatewithin the workpiece 102 around the irradiated spot location as a resultof thermal diffusion within the workpiece 102. Thus by the time thefinal spot location on the scan line is irradiated with one or morelaser pulses, a significant amount of heat will have been accumulated atthe final spot location. This thermal energy is believed to increase theefficiency with which material is removed from the workpiece 102. As aresult, after a number of laser pulses have been delivered along thescan line, the taper of the resultant sidewall formed in the workpiece102 at the final spot location on the scan line is relatively small.

The other of the factors relates to the temperature and pressureassociated with the vapor plume generated at a process spot whenmaterial is directly ablated from the workpiece 102. As the beam oflaser pulses is scanned along the scan line, the high temperature andpressure within the vapor plume can act to vaporize, melt or otherwiseerode material in the workpiece around the irradiated process spot. Itis suspected that this erosion is more vigorous if material around theirradiated process spot has already accumulated heat (e.g., generated byone or more previously-delivered laser pulses). The high pressurecreated by the resultant vapor plume acts to induce a hydrodynamicmotion to the eroded material, transporting the eroded material awayfrom the area within and around the irradiated process spot, thuscreating a sidewall within the workpiece 102 that has a relatively smalltaper. Furthermore, when laser pulses are delivered to one or more othersubsequently-irradiated spot locations along the scan line, erodedmaterial located within the trench can be advected or otherwisetransported towards a previously-irradiated spot location, possiblyincreasing the taper of a sidewall formed in the workpiece 102 at thepreviously-irradiated spot location. In FIG. 29B, sidewall 2902 having arelatively small taper can be characterized as being inclined (relativeto the bottom of trench 2900) at an angle Φ3 that is less than angle Φ2,which is the angle with which the sidewall 2904 (having a relativelylarge taper) can be characterized as being inclined relative to thebottom of trench 2900. The taper of the intermediate sidewall of thetrench 2900 (e.g., shown in cross-section in FIG. 29A), may vary fromthe beginning end to the terminal end of the trench 2900, as thelocation where the taper measurement moves from the beginning end to theterminal end. Thus, angle Φ1 may be equal to or less than angle Φ2. Insome embodiments, angle Φ1 may be greater than angle Φ2.

b. Sidewall Taper

The anisotropic material removal properties associated with thetrench-formation process discussed above, can be adapted to selected toaffect (e.g., reduce) the sidewall taper of a feature (e.g., an openingor via, as described above) or a trench, scribe line, recessed region,etc. For example, feature formation may be performed by scanning aprocess spot along one or more scan patterns as described above. In thepresent embodiment, however, the scan pattern includes one or moreanisotropic material removal scan lines. As a result, for a given spotsize, and depending upon one or more factors such as the depth of thefeature to be formed, the structure(s) in which the feature is formed,etc., the sidewall taper of a feature (e.g., a via, trench, scribe line,recessed region, etc.) that is formed by scanning a process spotaccording to a scan pattern having one or more anisotropic materialremoval scan lines (e.g., in the manner described with respect to scanpattern 2600) can be reduced relative to the sidewall taper of a featureformed simply by scanning a beam of laser pulses along a scan line thatmerely extends along a desired feature boundary (e.g., in the mannerdescribed with respect to scan patterns 2700 and 2800).

Conversely, and depending upon one or more factors such as the depth ofthe feature to be formed, the structure(s) in which the feature isformed, etc., the same sidewall taper obtained by scanning a beam oflaser pulses having a relatively small spot size along a scan lineextending along a desired feature boundary (e.g., in the mannerdescribed with respect to scan patterns 2700 and 2800) can be obtainedby scanning a beam of laser pulses having a relatively large spot sizeaccording to a scan pattern having one or more anisotropic materialremoval scan lines. When possible, it can be desirable to form featuresusing relatively larger spot sizes when: a) relatively large spot sizesare easier to form than relatively small spot sizes; b) relatively largespots are more tolerant to variations or deviations of worksurfaceZ-height outside nominal Z-height process windows (e.g., due to arelatively large Rayleigh range); and c) the deflection range ofpositioners such as AOD systems can be increased with relatively largerspot sizes (since AOD deflection, for a given update rate andpositioning bandwidth, is proportional to the spot size of laser pulsesdelivered to the workpiece 102).

As used herein, an anisotropic material removal scan line is a scan line(i.e., extending in a scanning plane which, in the embodimentillustrated in FIG. 29, is the X-Y plane) having an axis that intersectsthe desired feature boundary at an angle that, when measured within thescanning plane, is in a range from 60° to 120°. It should be recognizedthat the angle at which the axis of the anisotropic material removalscan line intersects the desired feature boundary can depend uponfactors such as spot size, type and shape of spatial intensity profile,the thermal conductivity, thermal diffusivity, specific heat capacity,etc., of the workpiece material at or near the spot locations to beirradiated with delivered laser pulses, the viscosity of the workpiecematerial at or near the spot locations to be irradiated with deliveredlaser pulses, pulse duration, fluence, pulse repetition rate, rate withwhich the process spot is moved along a process trajectory defining thescan pattern, or the like or any combination thereof. Thus, the angle atwhich the axis of the anisotropic material removal scan line canintersect the desired feature boundary can be less than 60° or greaterthan 120°. For example, the axis of a scan line can intersect thedesired boundary at an angle that is greater than or equal to 50°, 60°,65°, 70°, 75°, 80°, 85°, 87°, 88.5°, 90°, 91.5°, 93°, 95°, 100°, 105°,110°, 115°, 120°, etc., or between any of these values. Likewise, theaxis of the scan line can intersect the desired boundary at an anglethat is less than 130° 120°, 115°, 110°, 105°, 100°, 95°, 93°, 91.5°,90°, 88.5°, 87°, 85°, 80°, 75°, 70°, 65°, 60°, etc., or between any ofthese values.

In one embodiment, a pitch between adjacent terminal spot locations of apair of scan lines in a scan pattern is in a range from 0.5 μm to 50 μm,or may be less than 0.5 μm or greater than 50 μm. Thus, a pitch betweenadjacent spot locations 2504 (either within the scan pattern, generally,or disposed along a common scan line) may be greater than or equal to0.5 μm, 1 μm, 1.5 μm, 2 μm, 3 μm, 3.5 μm, 4.5 μm, 5 μm, 10 μm, 15 μm, 20μm, 30 μm, 40 μm, 55 μm, etc., or between any of these values, or lessthan 60 μm, 55 μm, 40 μm, 30 μm, 20 μm, 15 μm, 10 μm, 5 μm, 4.5 μm, 3.5μm, 3 μm, 2 μm, 1.5 μm, 1 μm, 0.5 μm, 0.1 μm, etc., or between any ofthese values. Two scan lines are considered to be adjacent to oneanother if no intervening scan line exists therebetween.

Scan pattern 2600, shown in FIG. 26, is an example of a scan patterncontaining a plurality of anisotropic material removal scan lines. Inthe scan pattern 2600, the scan line in region 2602 is an example of ananisotropic material removal scan line, and the spot location 2504 c isa terminal spot location of the anisotropic material removal scan line.Although FIG. 26 illustrates the scan pattern 2600 as including 27anisotropic material removal scan lines, it should be recognized thatscan patterns such as scan pattern 2600 can have more or fewer than 27anisotropic material removal scan lines (e.g., depending upon one ormore factors such as the shape of the desired boundary, the relativesize difference between the desired boundary and the spot size, the typeand shape of spatial intensity profile of delivered laser pulses, or thelike or any combination thereof).

Although FIG. 26 illustrates wherein each anisotropic material removalscan line includes the same arrangement of spot locations, it should berecognized that the arrangement of spot locations for one or more (orall) of the anisotropic material removal scan lines may be differentfrom the illustrated embodiment. Further the arrangement of spotlocations for one or more anisotropic material removal scan lines in ascan pattern may be the same as, or different from, the arrangement ofspot locations for at least one other anisotropic material removal scanline in the scan pattern. Thus, although FIG. 26 illustrates whereineach anisotropic material removal scan line includes 4 spot locations,it should be recognized that any anisotropic material removal scan linehave more or fewer than 4 spot locations. For example, the number ofspot locations that an anisotropic material removal scan line (such asthe anisotropic material removal scan line shown in region 2602) canhave can be 2, 3, 5, 6, 7, 8, 9, 10, or more.

iii. Considerations Regarding Localized Heat Accumulation

Depending upon one or more factors such as the wavelength, pulseduration, pulse repetition rate, average power, etc., of the laserpulses delivered to the workpiece 102, the linear absorption of amaterial at a spot location (e.g., relative to the wavelength of a laserpulse delivered to the spot location), the thermal conductivity, thermaldiffusivity, specific heat capacity, etc., of the material at or near aspot location, the scan pattern along which a process spot is to bescanned, or the like or any combination thereof, the heat generated as aresult of delivering laser pulses to one or more spot locations candiffuse from irradiated spot location and accumulate within regions ofthe workpiece 102 outside the process spot, thereby increasing thetemperature of the workpiece 102 at regions outside the process spot.

If the accumulated heat results in an increased temperature at a regionof workpiece 102 located at or near a to-be-addressed process spot, andif the increased temperature is above a threshold temperature (i.e., a“processing threshold temperature”), then the efficiency with which theworkpiece 102 can be subsequently processed (e.g., by direct ablation,indirect ablation, or any combination thereof) can be positivelyaffected. Generally, the processing threshold temperature associatedwith a material to be processed is greater than or equal to the meltingpoint or glass-transition temperature of the material to be processed.In another embodiment, however, the processing threshold temperature maybe less than (e.g., 98%, 95%, 93%, 90%, 89%, 87%, 85%, 80%, 75%, 70%,65%, or 50% of) the melting point or glass-transition temperature of thematerial to be processed.

In some cases, the accumulated heat can increase the temperature withinregions of the workpiece 102 that are not intended to be processed (eachalso referred to herein as a “non-feature region” of the workpiece 102).If the temperature is high enough, a non-feature region of the workpiece102 can become undesirably damaged (e.g., to become undesirably cracked,melted, delaminated, annealed, etc.). Thus it may be preferable toprocess the workpiece 102 in such a way that avoids undesirableaccumulation of heat within non-feature regions of the workpiece 102. Asused herein, the temperature at which a region of the workpiece 102 willbecome undesirably damaged is referred to as a “damage thresholdtemperature.” It should be recognized that the damage thresholdtemperature of any non-feature region of the workpiece 102 may dependupon one or more factors such as the thickness, thermal conductivity,thermal diffusivity, specific heat capacity, etc., optical absorptivity(relative to the beam of delivered laser energy), etc., of any materialat or near the spot location or in the non-feature region, as well asthe thermal conductivity, thermal diffusivity, specific heat capacity,size and shape of structures located within the vicinity of thenon-feature region, or the like or any combination thereof.

a. Leveraging Localized Heat Accumulation: Indirect Ablation

While considerations concerning the accumulation of heat can begenerally relevant depending upon characteristics of the workpiece 102,the manner in which the workpiece 102 is processed, etc., suchconsiderations can be particularly relevant when workpiece 102 isprocessed by indirect ablation. For example, when the workpiece 102 isprovided as a PCB including a dielectric structure (e.g., aglass-reinforced epoxy laminate) adhered to a first conductor (e.g., acopper or copper alloy foil) at a first side thereof and, optionally, toa second conductor (e.g., a pad, a trace, foil, etc., formed of copperor a copper alloy) at a second side thereof that is opposite the firstside, the workpiece 102 can be processed (e.g., by directing a beam oflaser pulses along the beam axis so as to deliver the laser pulses tothe workpiece 102) to indirectly ablate the first conductor, therebyforming an opening that exposes the dielectric structure.

In this example embodiment, the first conductor can have a thickness ina range from about 5 μm (or thereabout) to about 50 μm (or thereabout).For example, the first conductor can have a thickness equal (or aboutequal) to 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 15 μm, 17 μm, 18 μm, 20 μm, 25μm, 30 μm, 35 μm, 40 μm, etc., or between any of these values. Thedielectric structure can have a thickness in a range from 30 μm (orthereabout) to 200 μm (or thereabout). For example, the dielectricstructure can have a thickness equal (or about equal) to 50 μm, 60 μm,70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 140 μm, 180 μm, etc., orbetween any of these values. The opening formed by indirect ablation mayhave a top or bottom diameter in a range from 30 μm (or thereabout) to350 μm (or thereabout). For example, the top or bottom diameter of theopening may have a diameter equal (or about equal) to 30 μm, 40 μm, 50μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 150 μm, 200 μm,etc., or between any of these values.

According to one embodiment, the beam of laser pulses delivered to theworksurface 102 a (i.e., the first conductor) has a wavelength in thevisible green range of the electromagnetic spectrum, a Gaussian-type ornon-Gaussian-type spatial intensity profile, a pulse duration of greaterthan or equal to 1 ns (e.g., greater than or equal to 1 ns, 1.5 ns, 2ns, 2.5 ns, 5 ns, 7 ns, 10 ns, etc., or between any of these values), aspot size smaller than the top or bottom diameters of the opening to beformed (e.g., a spot size less than or equal to 30 μm, 25 μm, 20 μm, 15μm, 12 μm, 10 μm, 9 μm, 8 μm, 5 μm, etc., or between any of thesevalues), an average power greater than or equal to 100 W (e.g., greaterthan or equal to 120 W, 150 W, 180 W, 200 W, 225 W, 250 W, 275 W, 300 W,350 W, 500 W, etc., or between any of these values), and is delivered tothe worksurface 102 a at a pulse repetition rate greater than or equalto 100 MHz (e.g., greater than or equal to 125 MHz, 150 MHz, 175 MHz,200 MHz, 250 MHz, 300 MHz, 350 MHz, 500 MHz, etc., or between any ofthese values). Laser pulses having the above-described characteristicscan typically be generated by, or derived from, laser sources such as CWlaser sources, QCW laser sources, etc. Materials typically used to formthe first conductor (i.e. copper or a copper alloy) tend to absorb greenlight fairly efficiently. Accordingly, in the example given above,darkening of the exposed surface of the first conductor (i.e., thesurface of the first conductor facing away from the dielectricstructure)—a process typically used when indirectly ablating the firstconductor using laser pulses having a wavelength in the LWIR range ofthe electromagnetic spectrum—may be omitted if desired.

The beam axis can be moved (e.g., upon operation of the first positioner106) so as to scan the process spot along a scan pattern, such as scanpattern 2800, at a scan rate greater than or equal to 10 m/sec. (e.g.,greater than or equal to 12 m/sec., 13 m/sec., 14 m/sec., 15 m/sec., 16m/sec., 18 m/sec., 20 m/sec., etc., or between any of these values). Inone embodiment, the scan pattern 2800 fits entirely within the firstscanning range of the first positioner 106, but it will be appreciatedthat the scan pattern 2800 can be larger than the first scanning range.In this example, the pitch between adjacent spot locations 2504 in thescan pattern is constant, and the dwell time associated with each spotposition 2504 is the same as the dwell time associated with any otherspot position 2504 (e.g., greater than or equal to 1 μm, or thereabout).

Given the parameters in the above-described example, the first conductorcan be indirectly ablated to form an opening therein. During indirectablation, spot locations 2504 of the scan pattern 2800 are sequentiallyaddressed (i.e., by delivering one or more laser pulses thereto) togenerate and accumulate heat within the first conductor. The heatdissipates or is transferred from regions of the first conductor 102 atpreviously—and currently—addressed spot locations 2504 and accumulateswithin regions of the first conductor at one or more to-be-addressedspot locations 2504. Heat accumulating within a region of the firstconductor at a to-be-processed spot acts to increase the temperature ofthe first conductor at that region, and is also transferred into aregion of the dielectric structure therebeneath. Heat can alsoaccumulate within other regions of the first conductor, such as atpreviously-addressed spot locations 2504 (e.g., in the event that aregion of the first conductor at a previously-addressed spot location2504 has not already been indirectly ablated). During processing, heattransferred into the dielectric structure accumulates, and acts tovaporize a region of the dielectric structure below and adjoining aregion of the first conductor. If a region of the first conductor hasnot attained a temperature greater than or equal to its processingthreshold temperature before a region of the dielectric structuretherebelow has been vaporized, then vaporization of the region of thedielectric structure acts to create a pocket or space (e.g., ahigh-pressure region containing pressurized heated gas, particles, etc.,generated upon vaporization of the dielectric structure) beneath thefirst conductor. Then, when the region of the first conductor above thepocket attains a temperature greater than or equal to its processingthreshold temperature, pressure built up within the pocket acts to pushor eject the region of the first conductor from the workpiece 102 so asto expose the underlying dielectric structure.

A region of the first conductor above a pocket can be at ato-be-addressed spot location. In this case, when such region isultimately irradiated by one or more laser pulses, it can attain atemperature that is greater than or equal to the processing thresholdtemperature of the first conductor. In some cases, during processing, aregion of the first conductor above a pocket at a to-be-addressed spotlocation can attain a temperature that is greater than or equal to theprocessing threshold temperature of the first conductor after thatregion has accumulated heat dissipated from other previously- orcurrently-addressed spot locations. Also, in some cases duringprocessing, a region of the first conductor above a pocket can be at apreviously-addressed spot location. In this case, such a region canattain a temperature greater than or equal to the processing thresholdtemperature of the first conductor when it has accumulated heatdissipated from any other previously-addressed spot location, from acurrently-addressed spot location, or any combination thereof. Forexample, a pocket can be formed beneath a region of the first conductorat the first spot location 2504 a of scan pattern 2800, but such aregion of the first conductor might not attain a temperature greaterthan or equal to its processing threshold temperature until one or morespot locations such as spot locations 2504 e, 2504 f, etc., aresubsequently addressed.

In developing a process for indirectly ablating the first conductor byscanning the process spot along scan pattern 2800, it should berecognized that the minimum and maximum achievable diameter of theopening (at either the top or bottom of the first conductor) will dependupon one or more factors such as spot size, pulse duration, pulserepetition rate, average power, etc. of the delivered laser pulses, scanrate, thickness of the first conductor, thermal characteristics of thefirst conductor and the dielectric structure, the arrangement of spotlocations in scan pattern 2800, etc. For example, the minimum achievablediameter of an opening formed using delivered laser pulses of aparticular spot size will typically be limited to a range from 1.5 times(or thereabout) to 2 times (or thereabout) the particular spot size. Themaximum achievable diameter of an opening formed using delivered laserpulses of a particular spot size will typically correspond to themaximum diameter that can be obtained before any region within thefeature boundary 2502 (e.g., a central region thereof) cannot accumulatea sufficient amount of heat during processing to enable indirectablation. Thus, and depending upon one or more of the aforementionedfactors, scanning a beam of delivered laser pulses having a spot size of15 μm (or thereabout) along scan pattern 2800 can produce an opening inthe first conductor having a diameter in a range from 25 μm (orthereabout) to 80 μm (or thereabout). Likewise, if a spot size of 30 μm(or thereabout) is used, an opening having a diameter in a range from 60μm (or thereabout) to 200 μm (or thereabout). It should be recognizedthat an opening may be formed to have any diameter (e.g., regardless ofspot size used) by adding one or more additional spot locations to scanpattern 2800 (e.g., at a central region thereof) to ensure that allregions encompassed by a desired feature boundary 2502 accumulate asufficient amount of heat during processing to enable indirect ablation.

In the example embodiment described above, the first conductor isprocessed by scanning a process spot along scan pattern 2800 such thatthe pitch between adjacent spot locations 2504 is constant and the dwelltime associated with each spot position 2504 is the same as the dwelltime associated with any other spot position 2504. In other embodiments,however, parameters such as the dwell time, pitch, or the like or anycombination thereof, may be adjusted to control the manner with whichheat is accumulated within the first conductor. It should be recognizedthat the selection of such parameters (such as dwell time and pitch) inany scan pattern (including, but not limited to, scan pattern 2800) maybe dependent upon one or more factors such as the diameter of thedesired feature boundary 2502, the thickness of the first conductor, thethickness of the dielectric structure, the geometric configuration ofthe second conductor, the desired throughput of the process for formingthe opening in the first conductor, etc., the pulse duration, spot size,average power, etc., of laser pulses delivered to the first conductor,or the like or any combination thereof. Example embodiments concerningadjustment of some scanning technique parameters are discussed ingreater detail below. It should be recognized that these exampleembodiments may be implemented to control the manner with which heat isaccumulated within the workpiece 102, regardless of the type ofworkpiece 102 being processed or the feature(s) to be formed duringprocessing.

b. Controlling Localized Heat Accumulation: Dwell Time

In one embodiment, the dwell time associated with each spot location ina scan pattern (e.g., scan pattern 2500, 2600, 2700, 2800, or the like)is the same. In another embodiment, however, the dwell time associatedwith at least one spot location in a scan pattern is different from thedwell time associated with at least one spot location in the same scanpattern. Dwell time may be controlled by controlling an operation of thefirst positioner 106 (e.g., to scan the process spot within the firstscanning range), the second positioner 108 (e.g., to scan the processspot or the first scanning range within the second scanning range), bysuspending delivery of laser pulses to the workpiece 102 (e.g., using apulse gating unit, not shown), or the like or any combination thereof.

Differences in dwell time, as between different spot locations in acommon scan pattern or along a common scan line, can be selected,modulated or otherwise set to ensure that the temperature of theworkpiece 102 at one or more (or all) process spots of a scan patternwill be at or above the processing threshold temperature duringprocessing. For example, the dwell time associated with the first spotlocation of a scan pattern to be irradiated may be longer than the dwelltime associated with one or more (or all) other spot locations of thesame scan pattern. In another example, the dwell time associated withthe first spot location along a scan line to be irradiated (where suchspot location is not the first spot location in the scan pattern to beirradiated) may be equal to or longer than the dwell time associatedwith one or more (or all) other spot locations disposed along same scanline. In yet another example, the dwell time associated with any spotlocation along a scan line to be irradiated (where such spot location isnot the first spot location in the scan pattern to be irradiated) may beequal to or greater than the dwell time associated with an adjacent spotlocation (or any other spot location) disposed along same scan line tobe subsequently irradiated. In still another example, the dwell timeassociated with the first spot location along a particular scan line tobe irradiated (where such spot location is not the first spot locationin the scan pattern to be irradiated) may be equal to or longer than thedwell time associated with the first spot location along another scanline (which may or may not be adjacent to the first spot location of theparticular scan line) to be subsequently irradiated.

Differences in dwell time, as between different spot locations in acommon scan pattern or along a common scan line, can also be selected,modulated or otherwise set to ensure that the temperature of anon-feature region of the workpiece 102 will be at or below the damagethreshold temperature during processing of the workpiece 102. Forexample, the dwell time associated with the last spot location of a scanpattern to be irradiated may be shorter than the dwell time associatedwith one or more (or all) other spot locations of the same scan pattern.In another example, the dwell time associated with the last spotlocation along a scan line to be irradiated (where such spot location isnot the last spot location in the scan pattern to be irradiated) may beequal to or shorter than the dwell time associated with one or more (orall) other spot locations disposed along same scan line. In yet anotherexample, the dwell time associated with any to-be-addressed spotlocation along a scan line (where such spot location is not the firstspot location in the scan pattern) may be equal to or less than thedwell time associated with any other previously-addressed spot locationdisposed along same scan line. In still another example, the dwell timeassociated with the first spot location along one scan line to beirradiated (where such spot location is not the first spot location inthe scan pattern to be irradiated) may be equal to or longer than thedwell time associated with the first spot location along another scanline to be subsequently irradiated.

By lengthening the dwell time associated with one spot location relativeto one or more other spot locations in a scan pattern (or disposed alonga common scan line), the manner in which a region of the workpiece(e.g., at a previously-addressed, a currently-addressed, ato-be-addressed spot location, or the like or any combination thereof)accumulates heat (e.g., that was generated as a result of deliveringlaser pulses to one or more previously-addressed spot locations, as aresult of delivering laser pulses to a currently-addressed spotlocation, or any combination thereof) can be controlled to enableefficient ablation or other processing, while avoiding undesirabledamage to non-feature regions of the workpiece 102.

In view of the above, and continuing with the above-described exampleembodiment (i.e., in which an opening is formed in the first conductorof a PCB by indirect ablation), it should be recognized that the dwelltime associated with one or more spot locations 2504 of the scan pattern2800 may be different from any of the other the spot location 2504 ofthe scan pattern 2800. For example, the process spot can be scannedalong scan pattern 2800 such that the dwell time associated with firstspot location 2504 a of scan pattern 2800 is longer than the dwell timeassociated with all other spot locations 2504 of scan pattern 2800.Generally, the dwell time associated with first spot location 2504 a isset for a duration sufficient to ensure that the portion of the firstconductor at one or more spot locations 2504 to be addressed after thefirst spot location 2504 a (e.g., one or more of the second spotlocation 2504 e, the third spot location 2504 f, etc., in the scanpattern 2800) can be indirectly ablated when one or more of suchto-be-addressed spot locations 2504 are ultimately addressed.Optionally, the dwell time associated with the first spot location 2504a may be set such that the region of the first conductor at the firstspot location 2504 a is indirectly when the first spot location 2504 ais addressed. In general, however, the dwell time associated with eachof the spot locations 2504 can be set such that the temperature of anon-feature region of the workpiece 102 (e.g., any region within thedielectric structure adjoining or otherwise near the second conductor)remains below the damage threshold temperature during processing of thefirst conductor. In one embodiment, within scan pattern 2800, the dwelltime associated with the first spot location 2504 a, or any other spotlocation 2504 of scan pattern 2800, may be greater than or equal to theaforementioned positioning period of the first positioner 106. In oneembodiment, the dwell time associated with the first spot location 2504a may be in a range in a range from 2 μs (or thereabout) to 9 μs (orthereabout) (e.g., the dwell time associated with the first spotlocation 2504 a may be equal (or about equal) to 2 μs, 3 μs, 4 μs, 5 μs,6 μs, 7 μs, 8 μs, 9 μs, etc., or between any of these values). Inanother embodiment, the dwell time associated with spot locations 2504other than the first spot location 2504 a may be equal to 1 μs (orthereabout).

c. Controlling Localized Heat Accumulation: Pitch

In one embodiment, the pitch between adjacent spot locations in a scanpattern, between adjacent spot locations along a common scan line, orany combination thereof, is the same. In another embodiment, however,the pitch between one pair of adjacent spot locations and another pairof adjacent spot locations (i.e., in the same scan pattern, along acommon scan line, or any combination thereof) can be different. Pitchmay be controlled by controlling an operation of the first positioner106 (e.g., to scan the process spot within the first scanning range),the second positioner 108 (e.g., to scan the process spot or the firstscanning range within the second scanning range), the third positioner110 (e.g., to scan the first scanning range or the second scanning rangewithin the third scanning range), or the like or any combinationthereof.

Differences in pitch, as between different spot locations in a commonscan pattern or along a common scan line, can be selected, modulated orotherwise set to ensure that the temperature of the workpiece 102 at oneor more (or all) process spots of a scan pattern will be at or above theprocessing threshold temperature during processing. For example, thepitch between the first pair of adjacent spot locations in a scanpattern to be irradiated may be less than the pitch between one or more(or all) other pairs of adjacent spot locations of the same scanpattern. In another example, the pitch between the first pair ofadjacent spot locations along a scan line to be irradiated (where suchpair of adjacent spot locations is not the first pair of adjacent spotlocation in the scan pattern to be irradiated) may be equal to orshorter than the pitch between one or more (or all) other pairs ofadjacent spot locations disposed along same scan line. In yet anotherexample, the pitch between any pair of adjacent spot locations along ascan line to be irradiated (where such pair of adjacent spot locationsis not the first pair of adjacent spot locations in the scan pattern tobe irradiated) may be equal to or less than the pitch between any otherpair of adjacent spot locations disposed along same scan line to besubsequently irradiated. In still another example, the pitch between thefirst pair of adjacent spot locations along a particular scan line to beirradiated (where such pair of adjacent spot locations is not the firstpair of adjacent spot locations in the scan pattern to be irradiated)may be equal to or shorter than the pitch between another first pair ofadjacent spot locations along another scan line (which may or may not beadjacent to the first spot location of the particular scan line) to besubsequently irradiated.

Differences in pitch, as between different pairs of adjacent spotlocations in a common scan pattern or along a common scan line, can beselected, modulated or otherwise set to ensure that the temperature of anon-feature region of the workpiece 102 will be at or below the damagethreshold temperature during processing of the workpiece 102. Forexample, the pitch between a last pair of adjacent spot locations of ascan pattern to be irradiated may be longer than the pitch between oneor more (or all) other pairs of adjacent spot locations of the same scanpattern. In another example, the pitch between a last pair of adjacentspot locations along a scan line to be irradiated (where such pair ofadjacent spot locations is not the last pair spot location in the scanpattern to be irradiated) may be equal to or longer than the dwell timeassociated with one or more (or all) other spot locations disposed alongsame scan line. In yet another example, the pitch between any pair ofadjacent spot locations along a scan line to be irradiated (where suchspot location is not the first spot location in the scan pattern) may beequal to or longer than the pitch between any pair of adjacentpreviously-addressed spot locations disposed along same scan line. Instill another example, the pitch between the first pair of adjacent spotlocations along one scan line to be irradiated (where such pairs ofadjacent spot location is not the first pair of adjacent spot locationsin the scan pattern) may be equal to or shorter than the pitch betweenthe first pair of adjacent spot locations along another scan line of thescan pattern to be subsequently irradiated.

By shortening the pitch between with one pair of adjacent spot locationsrelative to one or more other pairs of adjacent spot locations in a scanpattern (or disposed along a common scan line), the manner in which aregion of the workpiece (e.g., at a previously-addressed, acurrently-addressed, a to-be-addressed spot location, or the like or anycombination thereof) accumulates heat (e.g., that was generated as aresult of delivering laser pulses to one or more previously-addressedspot locations, as a result of delivering laser pulses to acurrently-addressed spot location, or any combination thereof) can becontrolled to enable efficient ablation or other processing, whileavoiding undesirable damage to non-feature regions of the workpiece 102.

In view of the above, and continuing with the above-described exampleembodiment (i.e., in which an opening is formed in the first conductorof a PCB by indirect ablation), it should be recognized that the pitchbetween one or more pairs of adjacent spot locations 2504 of the scanpattern 2800 may be different from, or the same as, the pitch betweenany of the other pairs of adjacent spot location 2504 of the scanpattern 2800. For example, in one embodiment, the pitch between pairs ofadjacent spot locations in scan pattern 2800 can increase (e.g.,linearly or non-linearly, uniformly or non-uniformly, continuously ornon-continuously, etc.) from the first spot location 2504 a to the lastspot location 2504 b. In another embodiment, the pitch between pairs ofadjacent spot locations in one group of sequentially-addressable spotlocations in scan pattern 2800 can be different from the pitch betweenpairs of adjacent spot locations in any other group ofsequentially-addressable spot locations in scan pattern 2800. Forexample, the pitch between each of the pairs of adjacent spot locationsin a first group of sequentially-addressable spot locations in scanpattern 2800 can be less than the pitch between each of the pairs ofadjacent spot locations in a second group of sequentially-addressablespot locations in scan pattern 2800. Generally, spot locations in thefirst group of sequentially-addressable spot locations are addressedbefore spot locations in the second group of spot locations. Thus, thefirst group of sequentially-addressable spot locations includes, atleast, spot locations 2504 a, 2504 e and 2504 f, and the second group ofsequentially-addressable spot locations includes, at least spotlocations 2504 b, 2504 g and 2504 h. In one embodiment, the number ofspot locations in the first group of sequentially-addressable spotlocations is in a range from 1% to 95% of the total number of spotlocations of scan pattern 2800, and any spot locations not included inthe first group of sequentially-addressable spot locations are includedin the second group of sequentially-addressable spot locations.

In one embodiment, the pitch between each of the pairs of adjacent spotlocations in the first group of sequentially-addressable spot locationsis constant, and the number of spot locations in the first group ofsequentially-addressable spot locations is in a range from 1% to 95% ofthe total number of spot locations of scan pattern 2800. In thisembodiment, the number of spot locations in the first group ofsequentially-addressable spot locations is equal (or about equal) to 3%,5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc., or betweenany of these values).

iv. Other Considerations Concerning Scan Patterns

a. Single-Spot Location Scan Pattern

In the embodiments discussed above, a scan pattern has been described asincluding a plurality of sequentially-addressed spot locations, and theworkpiece 102 may be processed to form a feature by scanning a processspot along a scan pattern to irradiate the various spot locations. Inanother embodiment, however, a scan pattern may consist of only a singlespot location, and the workpiece 102 may be processed (e.g., ablated,marked, melted, etc.) simply by directing one or more laser pulses tothe single spot location (or otherwise delivered within a local vicinityof the single spot location). Such a scan pattern is herein referred toas a “single-spot location scan pattern.” For example, a single spotlocation of a scan pattern may be repeatedly irradiated with a pluralityof laser pulses to directly ablate the workpiece 102 (e.g., to form afeature such as a blind via, a through via, or other recess, hole oropening in the workpiece 102). This type of direct ablation process isoften referred to as a “punch” process.

In another example, when the workpiece 102 is provided as a PCB such asthat described above in the section “Leveraging Localized HeatAccumulation: Indirect Ablation,” the workpiece 102 can be processed todirectly or indirectly ablate the first conductor, thereby forming anopening that exposes a region of the dielectric structure. In oneembodiment, the laser pulses delivered to the single spot location canhave a wavelength in the UV range of the electromagnetic spectrum, andhave one or more other characteristics suitable to directly ablate thefirst conductor. In another embodiment, laser pulses delivered to thesingle spot location can have a wavelength in the long-wavelength IR(LWIR) range of the electromagnetic spectrum (i.e., such laser pulsesbeing typically generated from a carbon dioxide laser as laser source104), and have one or more other characteristics suitable to indirectlyablate the first conductor. In yet another embodiment, laser pulsesdelivered to the single spot location can have a wavelength in thevisible green range of the electromagnetic spectrum, and have one ormore other characteristics suitable to indirectly ablate the firstconductor.

Laser pulses having a wavelength in the visible green range of theelectromagnetic spectrum can often be produced at much higher averagepowers than corresponding laser pulses having a wavelength in the UVrange of the electromagnetic spectrum, enabling the workpiece 102 to beprocessed at a higher-throughput. Also, laser pulses having a wavelengthin the visible green range of the electromagnetic spectrum can befocused to a much smaller spot size than laser pulses having awavelength in the LWIR range of the electromagnetic spectrum, enablingsmaller features to be formed in the workpiece 102. Furthermore, and asnoted above, materials typically used to form the first conductor (i.e.copper or a copper alloy) tend to absorb green light fairly efficiently.Accordingly, darkening of an exposed surface of the first conductor(i.e., the surface of the first conductor facing away from thedielectric structure)—a process typically used when indirectly ablatingthe first conductor using laser pulses having a wavelength in the LWIRrange of the electromagnetic spectrum—may be omitted if desired.

Generally, the beam of laser pulses delivered to the worksurface 102 a(i.e., the first conductor) has a wavelength in the visible green rangeof the electromagnetic spectrum, a Gaussian-type or non-Gaussian-typespatial intensity profile, a pulse duration of greater than or equal to1 ns (e.g., greater than or equal to 1 ns, 1.5 ns, 2 ns, 2.5 ns, 5 ns, 7ns, 10 ns, etc., or between any of these values), a spot size smallerthan the top or bottom diameters of the opening to be formed (e.g., aspot size less than or equal to 30 μm, 25 μm, 20 μm, 15 μm, 12 μm, 10μm, 9 μm, 8 μm, 5 μm, etc., or between any of these values), an averagepower greater than or equal to 100 W (e.g., greater than or equal to 120W, 150 W, 180 W, 200 W, 225 W, 250 W, 275 W, 300 W, 350 W, 500 W, etc.,or between any of these values).

In one embodiment, the above-described green-wavelength laser pulses aredelivered to the worksurface 102 a (i.e., the first conductor) at apulse repetition rate greater than or equal to 100 MHz (e.g., greaterthan or equal to 125 MHz, 150 MHz, 175 MHz, 200 MHz, 250 MHz, 300 MHz,350 MHz, 500 MHz, etc., or between any of these values). Laser pulseshaving the above-described characteristics can typically be generatedby, or derived from, laser sources such as CW laser sources, QCW lasersources, etc. In other embodiments, however, other laser sources capableof producing green-wavelength laser pulses having pulse energies in therange from 100 μJ (or thereabout) to 50 mJ (or thereabout) over a timescale of one or more microseconds (e.g., a burst mode of ns or ps pulsesover multiple microseconds, or a burst mode where the burst is repeateditself every microsecond or less, etc.) may also be used to form anopening in the first conductor.

It should be recognized that the dwell time associated with the singlespot location may be in a range from 1 μs (or thereabout) to 30 μs (orthereabout), depending upon one or more factors such as thickness of thefirst conductor, surface absorption properties, certain laser parameters(e.g. pulse energy, pulse duration, pulse repetition rate, spot size andspot shape, etc.), and the like.

b. Sequential vs. Concurrent Feature Formation

In one embodiment, a beam of delivered laser pulses can be used to formmultiple features in or on a workpiece 102 in a sequential manner. Thatis, a beam axis along which a plurality of laser pulses are delivered tothe workpiece 102 is moved so as to scan a resultant process spot alonga first scan pattern, such as any of the scan patterns discussed aboveor any other scan pattern (or first set of such scan patterns) until afirst feature is formed. After the first feature is formed, the beamaxis is moved to another region of the workpiece 102 so as to scan aresultant process spot along a second scan, such as any of the scanpatterns discussed above or any other scan pattern (or second set ofsuch scan patterns) until a second feature is formed. One or moreadditional features may thereafter be sequentially formed in likefashion.

In another embodiment, a beam of delivered laser pulses can be used toform multiple features in or on a workpiece 102 in a concurrent manner.That is, a beam axis, along which a plurality of laser pulses aredelivered to the workpiece 102, is moved so as to alternately scan aresultant process spot along a multiple scan patterns. For example, thebeam axis may be moved such that one or more laser pulses are deliveredto one or more (but not all) spot locations of a first scan pattern and,thereafter, the beam axis is scanned such that one or more laser pulsesare delivered to one or more (but not all) spot locations of a secondscan pattern. The beam axis may then be moved such that one or morelaser pulses are delivered to one or more to-be-addressed spot locationsof the first scan pattern (or of the first set of scan patterns) or toone or more (but not all) spot locations of a third scan pattern (or ofa third set of scan patterns), etc. The process of moving the beam axisand alternately delivering laser pulses to one or more spot locations ofthe various scan patterns may be repeated until all spot locations ofthe first scan pattern (or first set of scan patterns) have beenaddressed (i.e., to form a first feature), until all spot locations ofthe second scan pattern (or second set of scan patterns) have beenaddressed (i.e., to form a second feature), etc. Forming multiplefeatures in a concurrent manner can be helpful in preventing non-featureregions of the workpiece 102 from becoming undesirably damaged due toheat that would otherwise accumulate during formation of a singlefeature or during sequential formation of multiple features.

Features which are either sequentially or concurrently formed asdescribed in the embodiments above may be the same or different from oneanother. At least some of the sequentially- or concurrently-formedfeatures may be spatially arranged relative to one another in or on theworkpiece 102 so as to be simultaneously arrangeable within the firstscanning range, within the second scanning range, or any combinationthereof. Thus, depending upon the size of the features ultimately formedand the distance between such features, the first scanning range or thesecond scanning range may encompass at least two sequentially- orconcurrently-formed features.

In one embodiment (e.g., when the workpiece 102 is provided as a PCBsuch as that described above in the section “Leveraging Localized HeatAccumulation: Indirect Ablation”), the workpiece 102 can be processed tosequentially or concurrently form multiple features, such as openings,in the first conductor by scanning the delivered laser pulses (e.g.,having characteristics as described in the section “Single-Spot LocationScan Pattern,” or having one or more other characteristics suitable tofacilitate indirect ablation of the first conductor) among differentsingle-spot location scan patterns. In another embodiment (e.g., whenthe workpiece 102 is provided as a dielectric structure such as abuild-up film, a glass-reinforced epoxy laminate, an interlayerdielectric material, a low-k dielectric material, a solder resist, orthe like or any combination thereof), the workpiece 102 can be processedto sequentially or concurrently form multiple features, such as one ormore vias (e.g., one or more blind vias or through vias), recesses,holes, openings, or the like or any combination thereof, by scanning abeam of delivered laser pulses (e.g., having one or more othercharacteristics suitable to facilitate direct ablation of the dielectricstructure) among different single-spot location scan patterns.Generally, laser pulses generated by burst mode lasers (or other lasersoperating in burst mode) will typically be generated at a pulserepetition rate lower than 100 MHz (i.e., often at or below 10 kHz).Accordingly, if laser pulses in either of the embodiments discussedabove are delivered to the worksurface 102 a at a pulse repetition rategreater than or equal to (or less than) 100 MHz, then multiple featuresmay be formed (i.e., either in the first conductor or in the dielectricstructure) by operating the first positioner 106 to scan the deliveredlaser pulses to different single-spot location scan patterns that aresimultaneously encompassed by the first scanning range. If laser pulsesare delivered to the worksurface 102 a at a pulse repetition rate of 10kHz or less, then multiple features may be formed by operating thesecond positioner 108 to scan the delivered laser pulses to differentsingle-spot location scan patterns that are simultaneously encompassedby the second scanning range.

VIII. Embodiments Concerning Modulation of Beam Characteristics

As mentioned above, a beam of laser energy (whether continuous orpulsed) delivered to the workpiece 102 during processing of theworkpiece 102 can characterized by one or more characteristics such aswavelength, average power, spatial intensity profile type, M² factor,spatial intensity profile shape, spot size, optical intensity, fluence,etc. When the beam of laser energy includes a one or more laser pulses,the beam can also be characterized by one or more characteristics suchas pulse repetition rate, pulse duration, pulse energy, peak power, etc.All of these characteristics of the beam of laser energy (whethercontinuous or pulsed) are herein generically and collectively referredto as “characteristics” of the beam of laser energy, or simply “beamcharacteristics.” Beam characteristics of laser pulses delivered to acommon spot location (or delivered to within the vicinity of a commonspot location) may be the same or different. For example, one or morecharacteristics such as spot size, pulse energy, pulse repetition rate,etc., of sequentially-delivered laser pulses delivered to a common spotlocation (or delivered to within the vicinity of a common spot locationmay be constant, may increase, may decrease, or any combination thereof.Likewise, beam characteristics of laser pulses delivered to differentspot locations of a common scan pattern may be the same or different.

Characteristics such as spot size may be adjusted by operating one ormore of the mechanisms for effecting Z-height compensation, describedabove. Characteristics such as M² factor and spatial intensity profileshape may be adjusted by operating one or more AOD systems (e.g.,whether provided as the first positioner 106, or otherwise) in themanner described above. Further, techniques discussed above with respectto operating an AOD system to change the M² factor can be modified toadjust the spatial intensity profile type of a beam of laser pulses, inthe manner discussed above. For example, the spectrum of an RF signal tobe applied to one or more transducers of an AOD system (e.g., whetherprovided as the first positioner 106, or otherwise) can be shaped tohave a non-Gaussian spectral profile (e.g., a rectangular or “top-hat”spectral profile). When such an RF signal is applied to one or moretransducers of an AOD system (e.g., whether provided as the firstpositioner 106, or otherwise), a laser pulse exiting the AOD system canbe changed in a manner that results in the generation of a laser pulsehaving a corresponding non-Gaussian spatial intensity profile type(e.g., a rectangular or “top-hat” spatial intensity profile). In oneembodiment, the spectrally-shaped RF signal is not chirped. In anotherembodiment, the spectrally-shaped RF signal may be chirped. Thus,depending upon the manner in which an AOD system is driven (i.e.,responsive to one or more applied RF signals), a laser pulse exiting theAOD system can be different from an incident laser pulse in terms of oneor more characteristics such as M² factor, spatial intensity profiletype, spatial intensity profile shape and spot size. These and otherbeam characteristics may also be changed in any other suitable ordesired manner that is either known in the art or otherwise disclosedherein (in this section or elsewhere).

Generally, one or more (or all) beam characteristics may be keptconstant (or at least substantially constant), may be modulated (e.g.,so as to be substantially non-constant), or any combination thereof,during processing of the workpiece 102. Example embodiments in which oneor more beam characteristics can be changed during processing of afeature are described below. Although particular embodiments concerningmodulation of beam characteristics are discussed in this section inconnection with apparatus 100, it will be appreciated that any one ofthese embodiments or any combination thereof, may be implemented inconnection with the multi-head apparatus 700. It will be furtherappreciated that the embodiments discussed in this section may beimplemented with any suitably-equipped single- or multi-headlaser-processing apparatus other than those discussed herein.

i. Feature Formation in Multilayered Workpieces

Workpieces having a multilayered construction can be processed to formone or more features that extend through multiple layers of theworkpiece. In one embodiment, a multilayered workpiece 102 may beprocessed to form a feature such as an opening, slot, via or other hole,groove, trench, scribe line, kerf, recessed region, etc., which extendsat least partially through two different layers of the multilayeredworkpiece 102. The different layers of the multilayered workpiece 102may be formed of different materials, have different optical absorptioncharacteristics (e.g., relative to the delivered beam of laser energy),or the like or any combination thereof. Accordingly, a feature may beformed in the multilayered workpiece 102 by ablating a first layer ofthe workpiece 102 using a beam of delivered laser energy characterizedby a first set of beam characteristics to, for example, expose a secondlayer of the workpiece 102. Thereafter, the second layer of theworkpiece 102 may be ablated using a beam of delivered laser energycharacterized by a second set of beam characteristics that is differentfrom the first set of beam characteristics (e.g., in terms ofwavelength, average power, spatial intensity profile type, M² factor,spatial intensity profile shape, spot size, optical intensity, fluence,pulse repetition rate, pulse duration, peak power, or the like or anycombination thereof). Any characteristic in the second set of beamcharacteristics may be the same as a corresponding characteristic in thefirst set of beam characteristics, so long as at least onecharacteristics is larger than, less than, or otherwise different from acorresponding characteristic in the first set of beam characteristics.

For example, a multilayered workpiece 102 may be provided as a PCB panelor PCB that includes a dielectric structure (e.g., a glass-reinforcedepoxy laminate) adhered to a first conductor (e.g., a copper or copperalloy foil, which may have an exposed surface that is eitherdarkened—e.g., by a chemical reaction, by a laser-darkening process,etc.—or that is not darkened) at a first side thereof and, optionally,to a second conductor (e.g., a pad, a trace, foil, etc., formed ofcopper or a copper alloy) at a second side thereof that is opposite thefirst side. The multilayered workpiece 102 may be processed to form avia extending completely through the first conductor and at leastpartially through the dielectric structure. The via may terminate at thesecond conductor (in which case the via is a blind via), or may extendcompletely through the second conductor (in which case the via may be athrough via).

In the example given above, a beam of laser energy characterized by afirst set of beam characteristics may be delivered to the firstconductor (e.g., and, optionally, scanned according a scan techniqueexemplarily described above) in a first processing step to directly orindirectly ablate the first conductor to form an opening that exposesthe dielectric structure. Thereafter, in a second processing step, abeam of laser energy characterized by a second set of beamcharacteristics may be delivered through the opening to the dielectricstructure (e.g., and, optionally, scanned according a scan techniqueexemplarily described above) to directly ablate the dielectric structureform a hole extending into the dielectric structure.

In one embodiment, the first and second sets of beam characteristics maybe same in terms of wavelength (e.g., the delivered beam of laser energymay have a wavelength in UV, visible or IR range of the electromagneticspectrum), but may differ in terms of fluence, optical intensity, or thelike or any combination thereof. For example, the fluence may be greaterduring the first processing step than during the second processing step.As between the first and second processing steps, the fluence may beadjusted by decreasing the pulse energy of the delivered beam of laserpulses, by increasing the spot size of the delivered beam of laserpulses, or the like or any combination thereof. For example, the spotsize of the beam of laser pulses delivered during the second processingstep (i.e., the “second spot size”) can be increased relative to thespot size of the beam of laser pulses delivered during the firstprocessing step (i.e., the “first spot size”) to reduce the fluence atthe process spot (e.g., below the threshold fluence at which materialsfrom which the first and second conductors are formed can be directlyablated) without reducing average power. As a result, the number ofnumber of pulses required to form the hole in the dielectric structurecan be kept relatively low and damage to neighboring conductorstructures can be avoided. In some embodiments, the first spot size maybe in a range from 2 μm (or thereabout) to 35 μm (or thereabout) and thesecond spot size, while being greater than the first spot size, may bein a range of from 40 μm (or thereabout) to 150 μm (or thereabout). Forexample, the first spot size may be equal (or about equal) to 2 μm, 3μm, 5 μm, 7 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, etc., orbetween any of these values, and the second spot size may be equal (orabout equal) to 40 μm, 50 μm, 60 μm, 80 μm, 100 μm, 125 μm, 140 μm, 155μm, etc.

ii. Considerations Regarding Localized Heat Accumulation

In one embodiment, one or more beam characteristics (e.g., pulse energy,pulse repetition rate, pulse duration, average power, or the like or anycombination thereof) may be selected, modulated or otherwise set toensure that the temperature of a non-feature region of the workpiece 102will be at or below the damage threshold temperature during processingof the workpiece 102 (e.g., over a period of time in which one or morefeatures are formed in the workpiece 102). Modulation of one or morebeam characteristics can be accomplished independently of parametersassociated with any scanning technique used to form a feature, or may beimplemented in conjunction with modulation of one or more scanningtechnique parameters (e.g., dwell time, pitch, or the like or anycombination thereof).

For example, and continuing with the above-described example embodimentin which an opening is formed in a first conductor of a PCB by indirectablation (e.g., by scanning a process spot along scan pattern 2800), thepulse energy of laser pulses delivered to the worksurface 102 a (i.e.,to the exposed surface of the first conductor) can be modulated suchthat the pulse energy of one or more laser pulses delivered to the lastspot location 2504 b of the scan pattern 2800 is less than the pulseenergy of one or more laser pulses delivered to the first spot location2504 a of the scan pattern 2800. For example, one or more laser pulsesdelivered to the last spot location 2504 b can have a pulse energy thatis in a range of 75% (or thereabout) to 20% (or thereabout) of the pulseenergy of one or more pulses delivered to the first spot location 2504 a(e.g., equal, or about equal, to 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%,40%, 35%, 30%, 25%, 20%, 15%, etc., or between any of these values, ofthe pulse energy of one or more pulses delivered to the first spotlocation 2504 a. In one embodiment, the pulse energy of laser pulsesdelivered to spot locations in scan pattern 2800 can decrease (e.g.,linearly or non-linearly, uniformly or non-uniformly, continuously ornon-continuously, etc.) from the first spot location 2504 a to the lastspot location 2504 b.

In another embodiment, the pulse energy of laser pulses delivered tospot locations in one group of sequentially-addressable spot locationsin scan pattern 2800 can be different from the pulse energy of laserpulses delivered to spot locations in any other group ofsequentially-addressable spot locations in scan pattern 2800. Forexample, the pulse energy of laser pulses delivered to spot locations ina first group of sequentially-addressable spot locations in scan pattern2800 can be greater than the pulse energy of laser pulses delivered tospot locations in a second group of sequentially-addressable spotlocations in scan pattern 2800. Generally, spot locations in the firstgroup of sequentially-addressable spot locations are addressed beforespot locations in the second group of sequentially-addressable spotlocations. Thus, the first group of sequentially-addressable spotlocations includes, at least, spot locations 2504 a, 2504 e and 2504 f,and the second group of sequentially-addressable spot locationsincludes, at least spot locations 2504 b, 2504 g and 2504 h. In oneembodiment, the number of spot locations in the first group ofsequentially-addressable spot locations is in a range from 1% to 95% ofthe total number of spot locations of scan pattern 2800, and any spotlocations not included in the first group of sequentially-addressablespot locations are included in the second group ofsequentially-addressable spot locations.

In one embodiment, the pulse energy of laser pulses delivered to spotlocations in the first group of sequentially-addressable spot locationsis constant, and the number of spot locations in the first group ofsequentially-addressable spot locations is in a range from 1% to 95% ofthe total number of spot locations of scan pattern 2800. In thisembodiment, the number of spot locations in the first group ofsequentially-addressable spot locations is equal (or about equal) to 3%,5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc., or betweenany of these values).

IX. Post-Processing

Sometimes, additional processing may be performed after a feature hasbeen formed (e.g., by scanning a process spot along one or morefeature-forming scan patterns, such as those described above, or alongone or more other scan patterns, or the like or any combinationthereof). Additional processing (e.g., in the presence of ambient air,an oxidizing gas or liquid, a reducing gas or liquid, an inert gas orliquid, a vacuum, etc.) may be performed to remove material (e.g.,residual material generated duration formation of a feature, orotherwise remaining on or within the feature after it has been formed)from a bottom surface of sidewall region of a feature, to further removeone or more portions of the workpiece 102 at the feature boundary (e.g.,to attain a feature boundary that more closely matches a desired featureboundary, etc.), to heat, anneal, melt, carbonize, oxidize, reduce,chemically etch or otherwise alter (e.g., using a light-activatedreactive agent, etc.), or otherwise treat one or more materials in whichthe feature is defined, or the like or any combination thereof.Accordingly, one or more post-processing techniques may be performed byscanning a process spot along one or more post-processing scan patterns,which may be the same as or different from any of the aforementionedfeature-forming patterns discussed above.

Generally, one or more characteristics of the post-processing scanpattern (e.g., including the arrangement of spot locations, theproximity of spot locations to the feature boundary, etc.), one or morebeam characteristics selected or otherwise used during post-processing,or the like or any combination thereof, may be same as, or differentfrom, corresponding characteristics of the feature-forming scan patternand may be the same as, or different from, corresponding characteristicsof the beam characteristics selected or otherwise used during formationof the feature. In one embodiment, one or more post-processingtechniques can be performed on a feature that has been formed, beforeforming another feature. In another embodiment however, one or morepost-processing techniques can be performed on a plurality of featuresonly after all of the plurality of features have been formed.

Example embodiments of post-processing techniques will now be discussedin greater detail below. Although particular embodiments concerningmodulation of beam characteristics are discussed in this section inconnection with apparatus 100, it will be appreciated that any one ofthese embodiments or any combination thereof, may be implemented inconnection with the multi-head apparatus 700. It will be furtherappreciated that the embodiments discussed in this section may beimplemented with any suitably-equipped single- or multi-headlaser-processing apparatus other than those discussed herein.

i. Via Cleaning

A feature such as a blind via may be formed in a workpiece by directlyablating a dielectric structure (e.g., a glass-reinforced epoxylaminate) to form therein a hole, which exposes, at a bottom portionthereof, a conductor (e.g., a pad, a trace, foil, etc., formed of copperor a copper alloy). Generally, the hole can be formed using a beam ofdelivered laser energy characterized by a first set of beamcharacteristics. Residual material (e.g., including resinous material)may remain within the blind via (e.g., on the exposed conductor), whichcan prevent reliable adhesion of subsequently a formed metallizationwithin the blind via, reduce the effective area at the bottom portion ofthe blind via available for electrical contact with the exposed copperlayer, etc. Accordingly, it can be beneficial to remove (eitherpartially or completely) the residual material. In one embodiment, theresidual material may be removed using a beam of delivered laser energycharacterized by a second set of beam characteristics that is differentfrom the first set of beam characteristics (e.g., in terms ofwavelength, average power, spatial intensity profile type, M² factor,spatial intensity profile shape, spot size, optical intensity, fluence,pulse repetition rate, pulse duration, peak power, or the like or anycombination thereof). Any characteristic in the second set of beamcharacteristics may be the same as a corresponding characteristic in thefirst set of beam characteristics, so long as at least onecharacteristics is larger than, less than, or otherwise different from acorresponding characteristic in the first set of beam characteristics.The beam of laser energy characterized by the second set of beamcharacteristics may be delivered into the opening formed in thedielectric structure to the exposed conductor and the residual materialarranged thereon. Such a beam of laser energy may, optionally, bescanned (e.g., according a scan technique exemplarily described above)to directly or indirectly ablate the residual material on the exposedconductor without ablating the exposed conductor.

In one embodiment, the first and second sets of beam characteristics maybe same in terms of wavelength (e.g., the delivered beam of laser energymay have a wavelength in UV, visible or IR range of the electromagneticspectrum), spatial intensity profile type (e.g., Gaussian-type spatialintensity profile), but may differ in terms of spot size, M² factor, orthe like or any combination thereof. For example, the spot size of thedelivered beam of laser energy during the second processing step may belarger than the spot size of the delivered beam of laser energy duringthe first processing step. Likewise, the M² factor of the delivered beamof laser energy may be adjusted to yield a delivered beam of laserenergy having a larger effective spot size during the second processingstep than during the first processing step. Adjustment of the spot sizeor the M² factor may be effected using any suitable or desired technique(e.g., as described above in the section “Embodiments ConcerningModulation of Beam Characteristics”). During the second processing step,the process spot may be scanned (e.g., so as to address to multiple spotlocations along a scan pattern) as desired. If the spot size (oreffective spot size) at the process spot during the second processingstep is sufficiently large, then the number of spot locations to addresswith the process spot may be reduced (e.g., to one or two spotlocations).

In another embodiment, the first and second sets of beam characteristicsmay be same in terms of wavelength (e.g., the delivered beam of laserenergy may have a wavelength in UV, visible or IR range of theelectromagnetic spectrum), but may differ in terms of spatial intensityprofile type, spatial intensity profile shape, spot size, or the like orany combination thereof. For example, the delivered beam of laser energyduring the first processing step may have a Gaussian-type spatialintensity profile with a generally circular shape, and have a relativelysmall spot size. However, the delivered beam of laser energy during thesecond processing step may have a non-Gaussian-type spatial intensityprofile (e.g., a “top-hat” spatial intensity profile, etc.) with a shapethat is circular or non-circular (e.g., square, etc.) and have arelatively large spot size. Adjustment of the spatial intensity profiletype, spatial intensity profile shape and spot size spot size may beeffected using any suitable or desired technique (e.g., as describedabove in the section “Embodiments Concerning Modulation of BeamCharacteristics”). During the second processing step, the process spotmay be scanned (e.g., so as to address to multiple spot locations alonga scan pattern) as desired. If the spot size (or effective spot size) atthe process spot during the second processing step is sufficientlylarge, then the number of spot locations to address with the processspot may be reduced (e.g., to one or two spot locations).

a. Blind Via Cleaning—Central Region

When forming features such as blind vias (e.g., through a dielectricstructure, to expose a copper layer at the bottom portion thereof),residual material (e.g., dielectric material) may be present at acentral region of the bottom portion of the blind via (e.g., on theelectrical conductor exposed at the bottom portion of the blind via).This may often be the case when using feature-forming scan patternscharacterized by relatively few (or no) spot locations located within acentral region of the desired feature boundary (e.g., as with scanpattern 2600 shown in FIG. 26).

To remove (either partially or completely) such residual material, apost-processing scan pattern (also referred to herein as a “centralregion cleaning scan pattern”) may be scanned. Generally, a centralregion cleaning scan pattern includes one or more spot locationsdisposed in a central region of the feature boundary at the bottomportion of the feature. FIG. 26 illustrates an example embodiment of acentral region cleaning scan pattern. The central region cleaning scanpattern include one or more spot locations (e.g., as shown in FIG. 26,the central region cleaning scan pattern includes multiple spotlocations 2504′) located within a central region of the feature boundary(e.g., within a central region of boundary 2502, which is encompassedwithin region 2602). Among the spot locations 2504′, spot location 2504a′ represents the first spot location to be irradiated with a laserpulse during the central region cleaning, and spot location 2504 b′represents the last spot location to be irradiated with a laser pulseduring the central region cleaning. Accordingly, the solid lineconnecting the spot locations 2504′ indicates the sequence in which thespot locations 2504 are addressed (e.g., by one or more delivered laserpulses). It should be recognized, however, that the spot locations 2504′may be addressed in any other desired sequence (thus changing theconfiguration of the solid line), and may even be addressed randomly.

Generally, laser pulses delivered to spot locations while scanning thecentral region cleaning scan pattern do not irradiate regions of theworkpiece 102 at the feature boundary. However, depending upon one ormore factors such as spot size, spatial intensity distribution, etc., ofthe delivered laser pulses, the size and shape of the feature boundaryat the top portion of the feature, the size and shape of the featureboundary at the bottom portion of the feature, the depth of the feature,etc., or the like or any combination thereof, one or more regions of theworkpiece 102 at the feature boundary (e.g., at or near the top portionof the feature) may be irradiated by at least a portion of at one ormore delivered laser pulses.

b. Blind Via Cleaning—Peripheral Region

When forming features such as blind vias (e.g., through a dielectricstructure, to expose a copper layer at the bottom portion thereof) usingscan patterns such as those described above with respect to FIGS. 25 to28, residual material (e.g., dielectric material) may be present at aperipheral region of the bottom portion of the blind via (e.g., at ornear a region where a sidewall of the blind via meets the electricalconductor exposed at the bottom portion thereof).

To remove (either partially or completely) such residual material, apost-processing scan pattern (also referred to herein as a “peripheralregion cleaning scan pattern”) may be scanned. The peripheral regioncleaning scan pattern may include one or more spot locations disposed ina peripheral region of the feature boundary at a bottom portion of thefeature. In one embodiment, the spot locations such as spot locations2504 a, 2504 b and 2504 d of scan pattern 2500, spot locations 2504 c ofscan pattern 2600, spot locations 2504 b and 2504 d of scan pattern 2700and spot locations 2504 of scan pattern 2800, etc., can be considered tobe located in a peripheral portion of the feature boundary at a bottomportion of the feature (if such scan patterns 2500, 2600, 2700 or 2800were actually scanned when the bottom portion of the feature wasformed). In another embodiment, spot locations of the peripheral regioncleaning scan pattern can be within a local vicinity of theaforementioned spot locations. For purposes of discussion, a spotlocation of the peripheral region cleaning scan pattern is considered tobe within a local vicinity of one of the aforementioned spot locationsif it is within 1 μm of one of the aforementioned spot locations (e.g.,within 0.8 μm, 0.75 μm, 0.7 μm, 0.65 μm, 0.6 μm, 0.5 μm, 0.4 μm, 0.3 μm,0.25 μm, 0.2 μm, 0.15 μm, 0.1 μm, 0.08 μm, 0.05 μm, 0.01 μm, or lessthan 0.01 μm, of one of the aforementioned spot locations). If both thecentral and peripheral regions of a blind via are to be cleaned, theperipheral region can be cleaned either before or after the centralregion is cleaned.

Generally, laser pulses delivered to spot locations while scanning theperipheral region cleaning scan pattern irradiate one or more regions ofthe workpiece 102 at the feature boundary (e.g., at or near the topportion of the feature). However, depending upon one or more factorssuch as spot size, spatial intensity distribution, etc., of thedelivered laser pulses, the size and shape of the feature boundary atthe top portion of the feature, the size and shape of the featureboundary at the bottom portion of the feature, the depth of the feature,etc., or the like or any combination thereof, laser pulses can bedelivered to spot locations of the central region cleaning scan patternso as to not irradiate regions of the workpiece 102 at the featureboundary.

ii. Fine-Tuning of Feature Boundary

In one embodiment, spot locations of the aforementioned scan patternsthat are adjacent to the desired feature boundary 2502 (e.g., spotlocations 2504 a, 2504 b and 2504 d of scan pattern 2500, spot locations2504 c of scan pattern 2600, spot locations 2504 b and 2504 d of scanpattern 2700 and spot locations 2504 of scan pattern 2800) are arrangedsufficiently close to the desired feature boundary so that, when one ormore laser pulses are delivered thereto, material is removed from theworkpiece 102 to form at least a portion of the desired feature boundary2502. In another embodiment, the material removed from the workpiece 102at such spot locations need not form a portion of the desired featureboundary. In either embodiment, a post-processing scan pattern includingone or more scan lines extending along at least a portion of the desiredfeature boundary (also referred to herein as a “boundary improvementscan pattern”) may be scanned (e.g., to, improve sidewall smoothness,improve fidelity of the feature boundary actually obtained to the shapeof the desired feature boundary, or the like or any combinationthereof).

iii. Timing for Post-Processing

In one embodiment, post-processing techniques such as those describedabove may be performed immediately after the feature has been formed.That is, a laser pulse may be delivered to the first spot location in apost-processing scan pattern immediately after the last laser pulse hasbeen delivered to a spot location in the feature-forming scan pattern.For example, boundary fine-tuning process or the central or peripheralregion cleaning processes can be performed immediately after a feature,such as a blind via, has been formed. In another embodiment, onepost-processing technique (e.g., the peripheral region cleaning process)may be performed immediately after another post-processing technique(e.g., the central region cleaning process) is completed. In thiscontext, “immediately after” means that the amount of time that elapsesbetween the completion of a feature-forming process (or anearlier-performed post-processing process) and a subsequently-performedpost-processing process is equal to (or at least substantially equal to)the shortest, longest, median or mean positioning period (e.g., of thefirst positioner 106 during the feature-forming process or theearlier-performed post-processing process). In one embodiment, thepositioning period of the first positioner 106 is less than 20 μs (orthereabout). For example, the positioning period of the first positioner106 can be less than or equal to 15 μs, 10 μs, 5 μs, 3 μs, 2 μs, 1 μs,0.8 μs, 0.5 μs, 0.3 μs, 0.1 μs, etc.

During feature formation, heat can accumulate within the workpiece 102in regions around where the feature is formed (e.g., due to theabsorption of energy in the delivered laser pulses by one or morematerials in the workpiece 102, due to the transfer of heat through oneor more materials in the workpiece 102, etc.). Accordingly, thetemperature of regions in the workpiece 102 around where a feature isformed can rise significantly during formation of the feature. When itis desired to remove material (e.g., material of a dielectric structure)from one or more regions in the workpiece 102 at the feature boundary(e.g., when post-processing to fine-tune the feature boundary), thisaccumulated thermal energy present in the material-to-be-removedadvantageously increases the post-processing efficiency.

However, when it is desired to remove material (e.g., residual material)at the bottom portion of a feature (e.g., when post-processing to cleanthe central or peripheral regions at the bottom portion of the feature),the accumulated thermal energy present in one or more regions of theworkpiece 102 (e.g., at or near the top portion of the feature) can makeit easier to remove portions of the workpiece 102 at or near the topportion of the feature if laser pulses, delivered to spot locationsduring the central or peripheral region cleaning, irradiate suchportions of the workpiece 102. As a result, the feature boundary at thetop portion of the feature can be undesirably widened during whilescanning a post-processing scan pattern such as a central regioncleaning scan pattern or a peripheral region cleaning scan pattern.

To overcome the above-described problem, a delay period may beinterposed between the completion of a feature-forming process (or anearlier-performed post-processing process) and a subsequently-performedpost-processing process such as a central region cleaning process or aperipheral region cleaning process. The duration of the delay period isselected or otherwise set to allow thermal energy within the workpiece102 (e.g., at or near the top portion of the feature) to dissipate(i.e., to allow regions of the workpiece 102 at or near the top portionof the feature to cool) so that portions of the workpiece 102 at or nearthe top portion of the feature are not removed upon being irradiated bylaser pulses delivered during the central or peripheral region cleaning.Generally, the delay period is longer than the shortest, longest, medianor mean positioning period (e.g., of the first positioner 106 during thefeature-forming process or the earlier-performed post-processingprocess). In one embodiment, and when the positioning period is lessthan 20 μs (or thereabout), the delay period is greater than 20 μs (orthereabout). For example, the delay period can be greater than or equalto 22 μs, 25 μs, 30 μs, 35 μs, 40 μs, 45 μs, 50 μs, 55 μs, 60 μs, etc.It should be recognized that the delay period can be selected orotherwise set depending upon one or more factors such as such as thermalconductivity, thermal diffusivity, specific heat capacity, viscosity,etc., of the material(s) of the workpiece 102 at or near the top portionof the feature, the pulse duration, fluence, pulse repetition rate,etc., of laser pulses delivered during the post-processing, the desiredthroughput for processing the workpiece 102 (which includes formation ofmultiple features, and performing post-processing, etc.), or the like orany combination thereof.

X. Embodiments Concerning Removal of By-Products

When one or more features such as an opening, slot, via, hole, groove,trench, scribe line, kerf, recessed region, etc., is formed within aworkpiece 102 as a result of laser-processing, byproduct materials suchas vapor (e.g., containing particles having a maximum cross-sectionaldimension ranging from about 0.01 μm to about 4 μm), dust (e.g.,containing particles having a maximum cross-sectional dimension rangingfrom about 0.1 μm to about 0.7 mm), workpiece fragments or other scrap(e.g., having a maximum cross-sectional dimension greater than about 0.7μm) can be generated. In some cases (e.g., during a drilling or cuttingprocess), such byproduct materials are ejected from the workpiece 102and re-deposited on the worksurface 102 a of the workpiece 102. In othercases (e.g., during a cutting process for forming a through hole orother feature extending through the workpiece 102), one more fragmentsor other scrap are not ejected from the workpiece 102 but, rather,simply remain stuck to the workpiece 102 (e.g., at a kerf formed in theworkpiece 102 during the cutting process). Depending upon the size ofthe through hole or other feature extending through the workpiece 102, afragment or other scrap of the workpiece 102 may have a maximumdimension that is significantly larger (e.g., by at least one order ofmagnitude) than the spot size of the laser energy delivered duringprocessing. To facilitate removal of such by-products, a byproductremoval system may be provided.

In one embodiment, and with reference to FIG. 38, the byproduct removalsystem may be provided as byproduct removal system 3800, which includesa frame 3802 for supporting a workpiece 102, an air knife 3804 arrangedover the frame 3802, and a collection bin 3806 arranged under the frame3802.

When supported by the frame 3802, the workpiece 102 (e.g., a PCB, anFPC, a lead frame blank, etc.) will have been processed and couldinclude vapor or dust that has settled on the worksurface 102 a. If theworkpiece 102 has been processed to form a through hole or other featureextending therethrough, then one more fragments or other scrap mayremain within the through hole or otherwise be stuck to the workpiece102 (e.g., at a kerf formed in the workpiece 102 during the cuttingprocess). The workpiece 102 may be transferred from the laser processingapparatus onto the frame 3802 by a transfer mechanism such as a roboticarm (e.g., having an end effector at an end thereof to engage with theworkpiece, etc.), a roll-to-roll handling system, or the like or anycombination thereof. In this case, the transfer mechanism may becontrolled in response to one or more control signals output by thecontroller 114, by another controller, or the like or any combinationthereof.

In one embodiment, the air knife 3804 is coupled to an actuator (notshown) and one or more linear stages or other mechanical linkages (e.g.,guide rails, etc.) that is operative to move the air knife 3804 over theworkpiece 102 (e.g., along the X-axis, as indicated by arrow 3808, alongthe Y-axis, or any combination thereof) while the workpiece 102 is keptstationary. In another embodiment, the frame 3802 is coupled to anactuator (not shown) and one or more linear stages or other mechanicallinkages (e.g., guide rails, etc.) that is operative to move the frame3802 (and, thus, the workpiece 102) beneath the air knife 3804 (e.g.,along the X-axis, as indicated by arrow 3808, along the Y-axis, or anycombination thereof). In either embodiment, the actuator may becontrolled in response to one or more control signals output by thecontroller 114, by another controller, or the like or any combinationthereof.

The air knife 3804 may be provided as a compressed air-powered airknife, a blower-powered air knife, or the like or any combinationthereof, and include a nozzle 3804 a configured to generate ahigh-pressure flow of air or other gas onto the worksurface 102 a withsufficient force to blow any settled dust or vapor particles off of theworksurface 102 a, to dislodge any fragments or other scraps stuck tothe workpiece 102, or the like. Dislodged fragments or other scraps(shown generally at 3810) fall into the collection 3806 (e.g., under theinfluence of gravity, the high-pressure flow generated by the air knife3804, or the like or any combination thereof). In one embodiment, anautomated optical inspection (AOI) system (not shown) may also beprovided to verify that by-products have been removed as desired. Theair knife 3804 and optional AOI system may be controlled in response toone or more control signals output by the controller 114, by anothercontroller, or the like or any combination thereof.

After the processed workpiece 102 has been subjected to thehigh-pressure flow generated by the air knife 3804, the workpiece 102may be transferred (e.g., to a storage bay of a material handlingapparatus such as the material handling apparatus 800, back to thelaser-processing apparatus for further processing, or the like).

XI. Embodiments Concerning Use of Multiple Laser Sources

Certain workpieces can be characterized as being heterogeneous incomposition or as being a composite material. Examples of suchworkpieces include PCB panels, PCBs, glass-reinforced epoxy laminates,prepregs, build-up materials, FPCs, ICs, ICPs, LEDs, LED packages, andthe like. Sometimes, such heterogeneous or composite workpieces(generically referred to herein as “compound workpieces”) are formed ofone or more components that are transparent to the wavelength of laserpulses delivered to the workpiece 102 (i.e., herein referred to as a“transparent workpiece component”), in addition to components that arenot transparent to the wavelength of laser pulses delivered to theworkpiece 102 (i.e., herein referred to as a “nontransparent workpiececomponent”). In this context, a component of the workpiece 102 may beconsidered a transparent workpiece component if it is formed of amaterial having a linear absorption spectrum within a particularbandwidth of the delivered laser pulses, and a thickness, such that thepercentage of light transmitted through the material (e.g., along thebeam axis) is greater than 10%, greater than 25%, greater than 50%,greater than 75%, greater than 80%, greater than 85%, greater than 90%,greater than 95%, greater than 98%, or greater than 99%.

As will be appreciated, it can be difficult to efficiently process acompound workpiece having a component made of a material that istransparent to the wavelength of the delivered laser pulses, especiallywhen the pulse duration of the delivered laser pulses is greater than afew tens of picoseconds. While use of “ultrashort” laser pulses (i.e.,laser pulses having a pulse duration less than a few tens ofpicoseconds, and often having a pulse duration in the femtosecond range)can effectively process transparent workpiece components via nonlinearabsorption, use of ultrashort laser pulses to process compoundworkpieces is not satisfactory either because the amount of materialremoved by each ultrashort laser pulse is relatively small. In view ofthese problems, some embodiments of the present invention provide anapparatus having multiple laser sources (also referred to herein as a“multi-source apparatus”) for processing a compound workpiece (formed ofboth transparent and nontransparent workpiece components).

For example, and with reference to FIG. 30, one embodiment of amulti-source apparatus, such as apparatus 3000, may include a firstlaser source 3002 a and a second laser source 3002 b. Generally, each ofthe first laser source 3002 a and the second laser source 3002 b areboth operative to generate laser energy sufficient to process thenontransparent workpiece component of a compound workpiece. In addition,the first laser source 3002 a is also generally operative to generatelaser energy sufficient to process the transparent workpiece componentof the compound workpiece.

Generally, each of the first laser source 3002 a and the second lasersource 3002 b may be provided as exemplarily described above withrespect to laser source 104. Accordingly, each of the first laser source3002 a and the second laser source 3002 b may include a pulse lasersource, a CW laser source, a QCW laser source, a burst mode lasersource, or the like or any combination thereof. In the event that eitherof the first laser source 3002 a or the second laser source 3002 bincludes a QCW or CW laser source, such laser source may, optionally,include a pulse gating unit (e.g., an acousto-optic (AO) modulator(AOM), a beam chopper, etc.) to temporally modulate beam of laserradiation output from the QCW or CW laser source. In one embodiment,each of the first laser source 3002 a and the second laser source 3002 bare provided as a pulse laser source. In another embodiment, the firstlaser source 3002 a is provided as a pulse laser source whereas thesecond laser source 3002 b is provided as a QCW or CW laser source andincludes a pulse gating unit to temporally modulate beam of laserradiation output from the QCW or CW laser source.

Depending upon the nature or composition of the various components inthe compound workpiece, the second laser source 3002 b may also beoperative to generate laser energy sufficient to process the transparentworkpiece component of the compound workpiece. For example if, duringprocessing of a compound workpiece (e.g., a glass-reinforced epoxylaminate) having a transparent workpiece component (e.g., glass fibers)embedded within (or otherwise in contact with) a nontransparentworkpiece component (e.g., a resin material), the nontransparentworkpiece component may be directly processed (e.g., melted, vaporized,ablated, carbonized, etc.) upon exposure to laser energy generated bythe first laser source 3002 a or the second laser source 3002 b. During,or as a result of, direct processing of the nontransparent workpiececomponent, the transparent workpiece component may become indirectlyprocessed. For example, the transparent workpiece component may becomecracked, heated, discolored (e.g., via a light- or heat-induced chemicalreaction between the transparent and nontransparent workpiececomponents), coated (e.g., with the nontransparent workpiece component,with a residue of the nontransparent workpiece component, etc.). Suchindirect processing of the transparent workpiece component mayfacilitate subsequent processing directly under the influence of laserenergy generated by the second laser source 3002 b. Depending upon thenature or composition of the various components in the compoundworkpiece, such subsequent direct processing may be substantial.

Generally, the first laser source 3002 a is operative to output laserpulses having a first pulse duration, and the second laser source 3002 bis operative to output laser pulses having a second pulse duration thatis greater than the first pulse duration. For example, the first pulseduration can be less than 500 ps (e.g., less than 450 ps, 25 ps, 15 ps,10 ps, 7 ps, 5 ps, 4 ps, 3 ps, 2 ps, 1 ps, 900 fs, 850 fs, 750 fs, 700fs, 500 fs, 400 fs, 300 fs, 200 fs, 150 fs, 100 fs, 50 fs, 30 fs, 15 fs,10 fs, etc., or between any of these values). In one embodiment, thesecond pulse duration can be greater than or equal to 500 ps (e.g.,greater than or equal to 600 ps, 700 ps, 800 ps, 900 ps, 1 ns, 1.5 ns, 2ns, 5 ns, 10 ns, 20 ns, 50 ns, 100 ns, 200 ns, 400 ns, 800 ns, 1000 ns,2 μs, 5 μs, 10 μs, 50 μs, 100 μs, 200 μs, 300 μs, 500 μs, 900 μs, 1 ms,2 ms, 5 ms, 10 ms, 20 ms, 50 ms, 100 ms, 300 ms, 500 ms, 900 ms, 1 s,etc., or between any of these values). In another embodiment, the secondlaser source 3002 b is provided as a QCW or CW laser source and does notinclude a pulse gating unit (e.g., such that the second laser source3002 b can generate a QCW or CW beam of laser energy).

Generally, the first laser source 3002 a is operative to output laserpulses at a first pulse repetition rate, and the second laser source3002 b is operative to output laser pulses at a first pulse repetitionrate that is greater than the first pulse repetition rate. For example,the second pulse repetition rate can be greater than or equal to 100 kHz(e.g., greater than or equal to 150 kHz, 250 kHz, 500 kHz, 800 kHz, 900kHz, 1 MHz, 2 MHz, 10 MHz, 20 MHz, 50 MHz, 70 MHz, 100 MHz, 150 MHz, 200MHz, etc., or between any of these values). In one embodiment, thesecond pulse repetition rate is equal to 150 MHz (or thereabout) and thefirst pulse repetition rate is equal to 1 MHz (or thereabout).Alternatively, the first laser source 3002 a and the second laser 3002 bmay be operative to output laser pulses at the same (or at leastsubstantially the same) pulse repetition rate.

In one embodiment, the first laser source 3002 a and the second lasersource 3002 b are operative to generate a beam of laser energy having atleast substantially the same wavelength(s), and at least substantiallythe same spectral bandwidth (i.e., as measured at FWHM). For example,the first laser source 3002 a and the second laser source 3002 b areoperative to generate a beam of laser energy having one or morewavelengths in the visible (e.g., green) range of the electromagneticspectrum. In another embodiment, at least one of the wavelength andspectral bandwidth of laser energy generated by the first laser source3002 a may be different from (e.g., greater than, less than, or anycombination thereof) the laser energy generated by the second lasersource 3002 b.

Although not illustrated, the apparatus 3000 also includes one or moreoptical components (e.g., beam expanders, beam shapers, apertures,harmonic generation crystals, filters, collimators, lenses, mirrors,polarizers, wave plates, diffractive optical elements, refractiveoptical elements, or the like or any combination thereof) to focus,expand, collimate, shape, polarize, filter, split, combine, crop, orotherwise modify, condition or direct laser energy generated by thefirst laser source 3002 a and propagating along a first preliminary beampath 3004 a. Likewise, the apparatus 3000 may include one or moreoptical components to focus, expand, collimate, shape, polarize, filter,split, combine, crop, or otherwise modify, condition or direct laserenergy generated by the second laser source 3002 b and propagating alonga second preliminary beam path 3004 b.

Laser energy propagating along the first preliminary beam path 3004 aand the second preliminary beam path 3004 b may be spatially combined inany suitable manner. For example, a fold mirror 3006 may be provided todirect the second preliminary beam path 3004 b into a beam combiner3008, which is also disposed in the first preliminary beam path 3004 a.Upon exiting the beam combiner 3008, laser energy can propagate alongbeam path 116 c (e.g., corresponding to the beam path 116 shown inFIG. 1) to a beam delivery system such as first beam delivery system3010.

Generally, the first beam delivery system 3010 may include one or morepositioners such as the aforementioned first positioner 106, theaforementioned second positioner 108, or any combination thereof,provided as exemplarily described above. In certain implementations,however, the beam combiner 3008 may alter a polarization state of laserenergy propagating along the first preliminary beam path 3004 a or thesecond preliminary beam path 3004 b. As a result, laser energypropagating along the beam path 116 c may be characterized by multiplepolarization states (e.g., p—polarization states, s—polarization states,etc., or between any of these values). In such implementations, thefirst beam delivery system 3010 does not include components that arerelatively sensitive to the polarization state of laser energy incidentthereto (e.g., an AOD system which is generally operationally sensitiveto laser energy having a linear polarization at a specific orientation).Rather, the first beam delivery system 3010 includes one or morecomponents that are relatively polarization-insensitive, such as agalvanometer mirror system, a MEMs mirror or mirror array, an FSM, orthe like or any combination thereof.

Although not illustrated, the apparatus 3000 may additionally includeone or more components such as aforementioned third positioner 110, ascan lens (e.g., aforementioned scan lens 112), controller (e.g.,aforementioned controller 114), or any other component previouslydiscussed with respect to apparatus 100 or 700, or the like or anycombination thereof.

In one embodiment, the controller 114 controls an operation of the firstlaser source 3002 a and the second laser source 3002 b to enable for thesetting of, or adjustment to, a temporal offset between (or temporaloverlap of) one or more laser pulses generated by the first laser source3002 a and one or more laser pulses generated by the second laser source3002 b. To facilitate such setting or adjustment, the apparatus 3000may, in one embodiment, further include one or more synchronizers,oscillators, etc., as described in International Patent App. Pub. No.WO2015/108991, which is incorporated herein by reference in itsentirety.

In another embodiment, the controller 114 does not control an operationof the first laser source 3002 a and the second laser source 3002 b toenable for the setting of, or adjustment to, a temporal offset between(or overlap of) any laser pulses generated by the first laser source3002 a and any laser pulses generated by the second laser source 3002 b.In this case, the apparatus 3000 does not include the synchronizers,oscillators, etc., as described in aforementioned International PatentApp. Pub. No. WO2015/108991. Rather, relative operational control of thefirst laser source 3002 a and the second laser source 3002 b is madewithout regard to the temporal relationship of laser pulses generated bythe first laser source 3002 a relative to the generation of laser energyby the second laser source 3002 b (which may be pulsed or continuous).Accordingly, the first laser source 3002 a may be operated to generatelaser energy independently of whether the second laser source 3002 b isoperated to generate laser energy. Trigger signals transmitted to thefirst laser source 3002 a and the second laser source 3002 b may besynchronized relative to one another in any suitable or desirablemanner, or may not be synchronized at all.

As mentioned above, laser energy propagating along the beam path 116 ccan contain multiple polarization states. Instead of limiting componentsin the first beam delivery system 3010 to those which are relativelypolarization-insensitive, a multi-source apparatus can be provided tomodify a polarization state of laser energy transmitted by the beamcombiner 3008. For example, and with reference to FIG. 31, oneembodiment of a multi-source apparatus, such as apparatus 3100, may beprovided as discussed above with respect to apparatus 3000, but mayfurther include a wave plate 3102 (e.g., a half-wave plate) disposed inbeam path 116 c to alter the polarization states of laser energytransmitted by the beam combiner 3008, and a polarizer 3104 to filter aportion of the laser energy transmitted by the wave plate 3102. Laserenergy transmitted by the polarizer 3104 can thereafter propagate alongbeam path 116 d (e.g., corresponding to the beam path 116 shown inFIG. 1) to the first beam delivery system 3010. In one embodiment, oneor both of the wave plate 3102 and the polarizer 3104 can be adjusted(e.g., rotated about the axis of beam path 116 c) to adjust the ratio ofthe amount of power within the beam of laser energy propagating alongbeam path 116 d, which originated from the first laser source 3002 a,versus that which originated from the second laser source 3002 b.Accordingly, laser energy propagating along the beam path 116 d cancontain a 50:50 mix of power originating from the first and second lasersources, respectively, or any other suitable or desired ratio (e.g.,60:40, 70:30, 80:20, 90:10, 10:90, 20:80, 30:70, 40:60, etc., or betweenany of these values). In the present embodiment, the first beam deliverysystem 3010 can be provided as discussed above with respect to theapparatus 3000, or may be provided to include one or morepolarization-sensitive components such as an AOD system as exemplarilydescribed above.

In another embodiment, and with reference to FIG. 32, one embodiment ofa multi-source apparatus, such as apparatus 3200, may be provided asdiscussed above with respect to apparatus 3100, but may further includea second beam delivery system 3202 optically coupled to the polarizer3104 (e.g., via beam path 116 d 2), whereas the first beam deliverysystem 3010 is optically coupled to the polarizer 3104 via beam path 116d 1. The second beam delivery system 3202 may be configured in the samemanner as (or different from) the first beam delivery system 3010. Inthe embodiment shown in FIG. 32, each of beam paths 116 d 1 and 116 d 2correspond to a different instance of the beam path 116 shown in FIG. 1.In this embodiment, the wave plate 3102 and polarizer 3104 (shown hereas a polarizing beam splitter cube) are configured such that each of thebeam paths 116 d 1 and 116 d 2 contain half (or at least roughly half)of the optical power originated from the first laser source 3002 a andhalf (or at least roughly half) of the optical power originated from thesecond laser source 3002 b. An additional wave plate 3204 (e.g., ahalf-wave plate) is disposed in beam path 116 d 1 to alter thepolarization state of laser energy transmitted by the polarizing beamsplitter cube 3104.

In another embodiment, within the apparatus 3200, the half-wave plate3102, the polarizer 3104 and the half-wave plate 3204 may be omitted andreplaced by a spinning chopper mirror, rotating polygon mirror, resonantgalvanometer mirror system, or the like or any combination thereof, todistribute laser energy along the beam paths 116 d 1 and 116 d 2. Inthis case, the first beam delivery system 3010 and the second beamdelivery system 3202 does not contain any polarization sensitivecomponents.

In another embodiment, and with reference to FIG. 33, one embodiment ofa multi-source apparatus, such as apparatus 3300, may include a beamdistributor 3302 configured to variously direct laser pulses output bythe first laser source 3002 a and the second laser source 3002 b to thefirst beam delivery system 3010, to the second beam delivery system3202, or any combination thereof. In this case, the beam distributor3302 may include an AO cell 3304, an ultrasonic transducer element 3306acoustically coupled to one side of the AO cell 3304, and an absorber3308 acoustically coupled to another side of the AO cell 3304 oppositethe ultrasonic transducer element 3306.

As illustrated, the first laser source 3002 a and the second lasersource 3002 b can be aligned (or one or more optical components can beprovided) such that laser pulses propagating along the first preliminarybeam path 3004 a and the second preliminary beam path 3004 b cancompletely (or at least substantially completely) overlap one another ata region (e.g., indicated by the black dot) within the AO cell 3304.Further, light within the laser pulses propagating along the firstpreliminary beam path 3004 a and the second preliminary beam path 3004 bcan be generated or otherwise conditioned by in any suitable manner tohave a polarization state necessary to be suitably diffracted within theAO cell 3304, to be suitably deflected by the first beam delivery system3010 or the second beam delivery system 3202.

The ultrasonic transducer element 3306 generates an acoustic wave withinthe AO cell 3304 upon being driven by an applied RF signal, where thepower of the applied RF signal is modulated (while maintaining aconstant RF frequency) to control the power of laser pulses deflectedwithin the AO cell 3304. In the absence of any applied RF signal, noacoustic wave is generated within the AO cell 3304 by the ultrasonictransducer element 3306, and any laser pulses generated by the firstlaser source 3002 a and the first laser source 3002 b, which areincident to the AO cell 3304, can pass through the AO cell 3304 torespective ones of the first beam delivery system 3010 and the secondbeam delivery system 3202. For example, in the absence of an RF signallaser applied to the ultrasonic transducer element 3306, laser pulsespropagating along the first preliminary beam path 3004 a are passed bythe AO cell 3304 to propagate along beam path 116 d 1 to the first beamdelivery system 3010 and, similarly, laser pulses propagating along thesecond preliminary beam path 3004 b are passed by the AO cell 3304 topropagate along beam path 116 d 2 to the second beam delivery system3202. Thus, beam path 116 d 1 constitutes the zeroth-order beam path forthe first laser source 3002 a and beam path 116 d 2 constitutes thezeroth-order beam path for the second laser source 3002 b.

When an RF signal having a first power level (e.g., a “full powerlevel”) is applied to the ultrasonic transducer element 3306, most ofthe power (e.g., about 90%) in the laser pulses propagating along thefirst preliminary beam path 3004 a is deflected by the AO cell 3304 topropagate along beam path 116 d 2 to the second beam delivery system3202 and, likewise, most of the power (e.g., about 90%) in the laserpulses propagating along the second preliminary beam path 3004 b aredeflected by the AO cell 3304 to propagate along beam path 116 d 1 tothe first beam delivery system 3010. In this case, a residual amount ofpower (e.g., about 10%) in the laser pulses propagating along the firstpreliminary beam path 3004 a is passed by the AO cell 3304 to propagatealong beam path 116 d 1 to the first beam delivery system 3010 and,likewise, a residual amount of power (e.g., about 10%) in the laserpulses propagating along the second preliminary beam path 3004 b ispassed by the AO cell 3304 to propagate along beam path 116 d 2 to thefirst second delivery system 3202.

In view of above, it will be appreciated that, when the ultrasonictransducer element 3306 is driven at full power, about 90% of the powerin laser pulses generated by the first laser source 3002 a and about 10%of the power in laser pulses generated by the second laser source 3002 bis delivered to the second beam delivery system 3202, while about 90% ofthe power in laser pulses generated by the second laser source 3002 band about 10% of the power in laser pulses generated by the first lasersource 3002 a is delivered to the first beam delivery system 3010. Theamount of power in the laser pulses generated by any single laser sourceand ultimately delivered to the first beam delivery system 3010 and thesecond beam delivery system 3202 can be further modulated by varying thepower of the RF signal applied to the ultrasonic transducer element3306. For example, when an RF signal having a second power level that is50% of the first power level is applied to the ultrasonic transducerelement 3306, about 50% of the power in laser pulses generated by thefirst laser source 3002 a and the second laser source 3002 b isdelivered to the first beam delivery system 3010 and to the second beamdelivery system 3202. The power level of the applied RF signal can bekept constant while the workpiece 102 is processed to form a feature, orcan be varied during the formation of an individual feature.

Although the multi-source apparatus 3300 has been described as includingboth the first beam delivery system 3010 and the second beam deliverysystem 3202, it will be appreciated that the multi-source apparatus 3300may include only the first beam delivery system 3010 or only the secondbeam delivery system 3202. In such a case, the omitted beam deliverysystem may be replaced by a beam dump.

Generally, the rate (also referred to as a “modulation rate”) with whichthe power of an applied RF signal can be varied to thereby modulate theamount power in laser pulses that is ultimately delivered to the firstbeam delivery system 3010 or the second beam delivery system 3202, fromeither the first laser source 3002 a or the second laser source 3002 b,is in a range from 50 kHz (or thereabout) to 10 MHz (or thereabout). Inone embodiment, the modulation rate is in a range from 100 kHz (orthereabout) to 2 MHz (or thereabout). In another embodiment, themodulation rate is 1 MHz (or thereabout). Thus, the relative powerlevels of laser pulses generated by the first laser source 3002 a andthe second laser source 3002 b that are ultimately delivered to eitherof the first beam delivery system 3010 or the second beam deliverysystem 3202 can be changed rapidly during processing of the workpiece102, simply by modulating the power level of the RF signal applied tothe ultrasonic transducer element 3306.

For example, if the first beam delivery system 3010 is to be used toform a feature such as a via (e.g., a blind via, a through via, etc.) ina multilayered workpiece including an electrical conductor structure(e.g., a film, foil, etc., which may be formed of copper, a copperalloy, etc.) provided (e.g., deposited, laminated, etc.) on a topsurface of a compound workpiece such as a glass-reinforced epoxylaminate material, then the power of an applied RF signal can beinitially set such that more than 50% (e.g., at least 55%, at least 60%,at least 75%, at least 80%, at least 85%, etc., or between any of thesevalues) of the power in laser pulses generated by the second lasersource 3002 b is delivered to the first beam delivery system 3010 toform an opening in the electrical conductor that exposes the compoundworkpiece. Thereafter, the power of an applied RF signal can be rapidlymodulated such that more than 50% (e.g., at least 55%, at least 60%, atleast 75%, at least 80%, at least 85%, etc., or between any of thesevalues) of the power in laser pulses generated by the first laser source3002 a is delivered to the first beam delivery system 3010 to form thevia in the compound workpiece.

XII. Embodiments Concerning Thermal Management

A. Thermal Management of Workpiece

Sometimes, during processing of a workpiece, the temperature of theambient environment in the vicinity of a worksurface 102 a of theworkpiece 102 can rise due to heat generating as a result oflaser-material interactions between the delivered laser pulses and theworkpiece. Such can be the case when performing a laser process such asvia drilling in workpieces such as PCB panels. If the temperature risebecomes high enough, the workpiece can undesirably expand, which candegrade the positional accuracy and precision with vias are drilled. Tohelp maintain the positional accuracy and precision with which vias aredrilled in the workpiece 102, the apparatus 100 can optionally beprovided with a temperature control system.

In one embodiment, the temperature control system includes a temperaturesensor 120 coupled to an input of the controller 114, and atemperature-controlled fluid nozzle 122. The temperature sensor 120 isconfigured to measure a temperature of (or a characteristic indicativeof the temperature of) the ambient environment (e.g., the ambient air)in the vicinity of the worksurface 102 a. The temperature-controlledfluid nozzle 122 is configured to induce a temperature-controlledgaseous flow (e.g., air) into the ambient environment within thevicinity of the worksurface 102 a. Typically, the temperature of thegaseous flow induced by the fluid nozzle 122 will be relatively coolcompared to the temperature measured by the temperature sensor 120.Thus, the gaseous flow can act to carry heat away from the ambientenvironment in the vicinity of the worksurface 102 a (and, consequently,to also carry away from the workpiece). In one embodiment, the apparatus100 may include a collection nozzle as disclosed in U.S. Patent App.Pub. No. 2014/0026351 (and the motive nozzle therein would delivertemperature-controlled fluid, thus acting as the temperature-controlledfluid nozzle described herein).

During operation, the temperature sensor 120 can generate one or moresignals (e.g., “temperature signals”) indicative of the measuredtemperature (or characteristic thereof) and output the same to thecontroller 114. The controller 114 can process the temperature signal(s)to determine whether or not the measured temperature is outside apredetermined nominal temperature process window (e.g., ±10 degreesCelsius, ±5 degrees Celsius, ±2 degrees Celsius, etc.). If the measuredtemperature is determined to be outside the nominal temperature processwindow (e.g., higher than the nominal temperature process window), thenthe controller 114 can generate and output one or more control signalsto the temperature-controlled fluid nozzle 122 to induce a fluid flowhaving a temperature that is different from (e.g., lower than) themeasured temperature to bring the temperature of the ambient environmentwithin the vicinity of the worksurface 102 a back to within the nominaltemperature process window. In the illustrated embodiment, thecontroller 114 can be considered to be part of the temperature controlsystem insofar as it is communicatively coupled to the temperaturesensor 120 and the fluid nozzle 122. In other embodiments, however, thetemperature sensor 120 and the fluid nozzle 122 may be coupled to adifferent controller (not shown, but having a construction and operationthat is the same or similar to that of the controller 114) associatedwith the temperature control system. Although the temperature controlsystem has been described as being an optional component of theapparatus 100, it will be appreciated that the temperature controlsystem may be incorporated into another apparatus (either alaser-processing apparatus or otherwise) other than the apparatus 100.

B. Thermal Management of the AO Cell

As mentioned above, acoustic waves are typically launched into an AOcell by driving an ultrasonic transducer element, acoustically coupledto one end of the AO cell (also referred to as a “connector end”), atone or more RF frequencies. An example AO device (i.e., which may be anAOM, an AOD, etc.) having the construction described above is shown inFIGS. 34 and 35. Referring to FIGS. 34 and 35, an exemplary AO device3400 includes an AO cell 3402, an ultrasonic transducer element 3404acoustically coupled to a connector end of the AO cell 3402, and anabsorber 3406 acoustically coupled to an absorber end of the AO cell3402, opposite the connector end. In FIGS. 34 and 35, a beam of laserenergy 3408 is illustrated as entering into the AO cell 3402 through aninput face thereof.

Acoustic waves propagating through the AO cell 3402 generate heat, whichis beneficially extracted to prevent the AO cell 3402 from degrading(e.g., optically, physically, etc.). A common method of cooling the AOcell 3402 is to attach cooling plates to the AO cell 3402 at positionswhich will not interfere with the propagation of optical waves from theinput face to output face of the AO cell. For example, and withreference to FIGS. 34 and 35, a first cooling plate 3408 may bethermally coupled to a first thermal extraction face of the AO cell3402, and a second cooling plate 3410 may be thermally coupled to asecond thermal extraction face of the AO cell 3402 that is opposite thefirst thermal extraction face. Generally, the first and second thermalextraction faces can be characterized as oppositely-situated faces (orfacets) of the AO cell 3402, which are not covered by the ultrasonictransducer element 3304 or the absorber 3406. Also, the beam of laserenergy does not typically propagate through the first and second thermalextractions faces.

Generally, the AO cell 3402 can have a length dimension (i.e., asmeasured from the input face to the output face), in a range from 15 mm(or thereabout) to 35 mm (or thereabout). In one embodiment, the lengthof the AO cell 3402 can be in a range from 18 mm to 30 mm. In anotherembodiment, the length of the AO cell 3402 is in a range from 20 mm to30 mm. In yet another embodiment, the length of the AO cell 3402 is in arange from 22 mm to 28 mm. It should be recognized, however, that the AOcell 3402 can have a length that is less than 15 mm, or greater than 30mm.

Generally, the AO cell 3402 can have a thickness dimension (i.e., asmeasured from the first thermal extraction face to the second thermalextraction face), in a range from 15 mm (or thereabout) to 35 mm (orthereabout). In one embodiment, the thickness of the AO cell 3402 can bein a range from 18 mm to 30 mm. In another embodiment, the thickness ofthe AO cell 3402 is in a range from 20 mm to 30 mm. In yet anotherembodiment, the thickness of the AO cell 3402 is in a range from 22 mmto 28 mm. It should be recognized, however, that the AO cell 3402 canhave a thickness that is less than 15 mm, or greater than 30 mm. Itshould also be recognized that thickness of the AO cell 3402 can begreater than, equal to, or less than the length of the AO cell 3402.

Generally, the AO cell 3402 can have a width dimension (i.e., asmeasured from the connector end to the absorber end), in a range from 15mm (or thereabout) to 35 mm (or thereabout). In one embodiment, thewidth of the AO cell 3402 can be in a range from 18 mm to 30 mm. Inanother embodiment, the width of the AO cell 3402 is in a range from 20mm to 30 mm. In yet another embodiment, the width of the AO cell 3402 isin a range from 22 mm to 28 mm. It should be recognized, however, thatthe AO cell 3402 can have a width that is less than 15 mm, or greaterthan 30 mm. It should also be recognized that width of the AO cell 3402can be greater than, equal to, or less than any of the length orthickness of the AO cell 3402.

The first cooling plate 3408 and the second cooling plate 3410 aregenerally cooled by flowing water through one or more channels formedtherein. For example, and with reference to FIG. 35, first cooling plate3408 and second cooling plate 3410 each include a cooling channel formedtherein (e.g., a U-shaped channel, where only the ends of the channelsare shown). In FIG. 35, ends 3502 a and 3502 b are input and outputends, respectively, of a cooling channel formed in first cooling plate3408. Likewise, ends 3504 a and 3504 b are input and output ends,respectively, of a cooling channel formed in the second cooling plate3410. A pump (not shown) can be provided to generate a flow of coolant(e.g., water) through each cooling channel (e.g., such that coolantenters a cooling channel through an input end 3502 a or 3504 a, andexits the cooling channel through an output end 3502 b or 3504 b,respectively, to remove heat from the AO cell 3402.

Cooling plates such as those described above are configured to removeroughly the same amount of heat from the center of the AO cell 3402 asthey do from the connector and absorber ends. However, the amount ofheat generated at the connector end of the AO cell 3402 can be highcompared to a central region of the AO cell 3402, and can be even higherat the absorber end of the AO cell 3402. Thermal gradients may, to alesser extent, also be present across the length and thicknessdimensions of the AO cell 3402. Sufficiently large thermal gradientswithin the AO cell 3402 can cause undesirable thermal lensing effects,deterioration in diffraction efficiency, deflection errors, etc.

Conventionally, deleterious effects associated with undesirably largethermal gradients within the AO cell 3402 are minimized or avoided byconfining the beam of laser energy propagating through the AO cell 3402to within a relatively small volume (also referred to herein as a“working volume”) of the AO cell 3402 (e.g., measuring 4 mm to 5 mm, inthe width dimension). However, it would be desirable to increase theworking volume of the AO cell 3402, at least in the width dimension.Thus, in accordance with some embodiments, an AO device is configured toprovide for non-uniform heat removal, wherein less heat is removed fromthe central region of the AO cell 3402 than from peripheral regions ofthe AO cell 3402 (i.e., regions of the AO cell 3402 at or near theconnector end, at or near the absorber end, or any combination thereof.

In some embodiments, non-uniform heat removal is accomplished byproviding, instead of a cooling plate such as the first cooling plate3408 or the second cooling plate 3410, a “non-uniform” cooling plateconfigured to remove less heat from the central region of the AO cell3402 than from one or more peripheral regions of the AO cell 3402.

For example, a non-uniform cooling plate can be provided with one ormore grooves, pits, etc., formed in a thermal extraction surface thereof(e.g., a surface which forms a thermal interface with the first orsecond thermal extraction face of the AO cell 3402) at a locationcorresponding to the central region of the AO cell 3402. When disposedin the thermal contact with a thermal extraction face of the AO cell3402, the one or more grooves, pits, etc., help define voids within thecentral region of the AO cell 3402, which act as impediments thermaltransfer (i.e., relative to the thermal interface between the AO cell3402 and the non-uniform cooling plate). See, e.g., FIG. 36.

In another example, a non-uniform cooling plate can be provided with oneor more voids, channels, etc., formed within the interior thereof (e.g.,spaced apart from the thermal extraction surface) at a locationcorresponding to the central region of the AO cell 3402. When disposedin the thermal contact with a thermal extraction face of the AO cell3402, the one or more voids, pits, etc., act as impediments to thermaltransfer from the central region of the AO cell 3402. See, e.g., FIG.36.

In another example, a non-uniform cooling plate can be provided with oneor more voids, channels, etc., formed within the interior thereof (e.g.,spaced apart from the thermal extraction surface), as well as groovesformed in the surface thereof, at a location corresponding to thecentral region of the AO cell 3402, resulting in a so-called “thermalchoke” structure that has a reduced capacity to conduct transfer heatfrom the AO cell 3402. An example of such as thermal choke structure,which is composed of cooling path conduits, is illustrated in FIG. 37.

In yet another example, a non-uniform cooling plate can be formed ofmultiple materials having different heat transfer characteristics. Forexample, the non-uniform cooling plate can be formed of a first materialhaving a first thermal conductivity at a location corresponding to thecentral region of the AO cell 3402, and a second material having asecond thermal conductivity (higher than the first thermal conductivity)at one or more locations corresponding to a peripheral region of the AOcell 3402.

In still another example, a non-uniform cooling plate can include one ormore cooling channels, formed as discussed above, but more coolingchannels may be located at a region of the cooling plate correspondingto a peripheral region of the AO cell 3402 than at a region of thecooling plate corresponding to the central region of the AO cell 3402.In one implementation, the non-uniform cooling plate can contain nocooling channels in a region of the cooling plate corresponding to acentral region of the AO cell 3402.

In yet another example, a non-uniform cooling plate can include one ormore cooling channels, formed as discussed above, but the flow rate ofcoolant through one or more cooling channels located at a region of thecooling plate corresponding to the central region of the AO cell 3402may be lower than a flow rate of coolant through one or more coolingchannels located at a region of the cooling plate corresponding to aperipheral region of the AO cell 3402.

In another example, a non-uniform cooling plate may simply be configuredso as to thermally contact a thermal extraction face at one or morelocations corresponding to a peripheral region of the AO cell 3402, butnot at a location corresponding to the central region of the AO cell3402.

In another embodiment, non-uniform heat removal can be accomplished byproviding a cooling plate in thermal contact with a thermal extractionface of the AO cell 3402 only at a region corresponding to a peripheralregion of the AO cell 3402, by providing a heating element in thermalcontact with the thermal extraction face at a location corresponding tothe central region of the AO cell 3402, or any combination thereof. Inthis embodiment, the heating element acts to heat the central region ofthe AO cell 3402 so as to reduce the temperature difference(s) withinthe AO cell 3402 between the central region and one or more of theperipheral regions thereof.

XIII. Conclusion

The foregoing is illustrative of embodiments and examples of theinvention, and is not to be construed as limiting thereof. Although afew specific embodiments and examples have been described with referenceto the drawings, those skilled in the art will readily appreciate thatmany modifications to the disclosed embodiments and examples, as well asother embodiments, are possible without materially departing from thenovel teachings and advantages of the invention. Accordingly, all suchmodifications are intended to be included within the scope of theinvention as defined in the claims. For example, skilled persons willappreciate that the subject matter of any sentence, paragraph, exampleor embodiment can be combined with subject matter of some or all of theother sentences, paragraphs, examples or embodiments, except where suchcombinations are mutually exclusive. The scope of the present inventionshould, therefore, be determined by the following claims, withequivalents of the claims to be included therein.

What is claimed is:
 1. An apparatus for laser-processing a workpiececomprising an electrical conductor structure in thermal contact with adielectric structure, the apparatus comprising: a laser sourceconfigured to generate a plurality of laser pulses; a scan lens arrangedin a beam path along which the plurality of laser pulses are directableto the workpiece to thereby irradiate a process spot at the workpiece; afirst positioner including an acousto-optical deflector (AOD) systemarranged along the optical path between the laser source and the scanlens, wherein the first positioner is operative to deflect the pluralityof laser pulses relative to the scan lens; a controller communicativelycoupled to the first positioner and configured to control an operationof the first positioner, wherein the controller includes: a processorconfigured to generate one or more control signals to which the firstpositioner is responsive; and computer memory accessible by theprocessor, wherein the computer memory has instructions stored thereonwhich, when executed by the processor, cause the first positioner toscan the process spot along a process trajectory to form a via in theworkpiece, wherein the process trajectory defines a sequence of spotlocations to be addressed upon irradiating the workpiece with theplurality of laser pulses during formation of the via and wherein thecontroller is configured to control the operation of the firstpositioner to form the via such that the laser pulses irradiating theworkpiece at the sequence of spot locations: a) vaporize a first regionof the dielectric structure at the surface, thereby generating ahigh-pressure region between the first region of the dielectricstructure and a first region of the electrical conductor structure, andb) heat the first region of the electrical conductor structure such thatat least a portion of the heated first region of the electricalconductor structure is ejectable from the workpiece by the high-pressureregion.
 2. The apparatus of claim 1, wherein the laser pulses have awavelength of less than 1 μm.
 3. The apparatus of claim 2, wherein thelaser pulses are delivered to the workpiece at a pulse repetition rategreater than or equal to 100 MHz.
 4. The apparatus of claim 1, whereinthe laser pulses have a pulse duration greater than or equal to 1 ns. 5.The apparatus of claim 1, wherein the laser pulses have an average powergreater than or equal to 100 W.
 6. The apparatus of claim 1, wherein apulse repetition rate at which laser pulses irradiate the workpiece isgreater than a rate with which different spot locations of the sequenceof spot locations are addressed.
 7. The apparatus of claim 1, wherein apulse repetition rate at which laser pulses irradiate the workpiece isequal to a rate with which different spot locations of the sequence ofspot locations are addressed.
 8. The apparatus of claim 1, wherein apulse repetition rate at which laser pulses irradiate workpiece is lessthan a rate with which different spot locations of the sequence of spotlocations are addressed.
 9. The apparatus of claim 1, wherein the firstpositioner is operated to scan the process spot such that a differentspot location of the sequence of spot locations is addressed at a ratein a range from 50 kHz to 10 MHz.
 10. The apparatus of claim 9, whereinthe rate is greater than 1 MHz.
 11. The apparatus of claim 1, wherein apitch between one pair of adjacent spot locations in the sequence ofspot locations is equal to a pitch between another pair of adjacent spotlocations in the sequence of spot locations.
 12. The apparatus of claim1, wherein a pitch between one pair of adjacent spot locations in thesequence of spot locations is different from a pitch between anotherpair of adjacent spot locations in the sequence of spot locations. 13.The apparatus of claim 1, wherein a period of time during which one spotlocation of the sequence of spot locations is irradiated by laser energyis equal to a period of time during which another spot location of thesequence of spot locations is irradiated by laser energy.
 14. Theapparatus of claim 1, wherein a period of time during which one spotlocation of the sequence of spot locations is irradiated by laser energyis different from a period of time during which another spot location ofthe sequence of spot locations is irradiated by laser energy.
 15. Theapparatus of claim 1, wherein the process trajectory defines a sequenceof spot locations arranged in a circular scan pattern.
 16. The apparatusof claim 1, wherein the controller is configured to control theoperation of the first positioner to form the via such that the laserpulses irradiating the workpiece at the sequence of spot locations heatthe first region of the electrical conductor structure to at least 50%of the melting point of the electrical conductor structure.
 17. Anapparatus for processing a workpiece comprising an electrical conductorstructure in thermal contact with a dielectric structure, the apparatuscomprising: a laser source operative to generate a beam of laser energycomprising a plurality of laser pulses, wherein laser pulses of theplurality of laser pulses have a wavelength of less than 1 μm and apulse energy in a range from 100 μJ to 50 μJ over a time scale of atleast one microsecond; a positioner arranged within a beam path alongwhich the beam of laser energy can propagate to the workpiece andirradiate the workpiece, wherein the first positioner is operative toimpart movement of the beam path relative to the workpiece; a controllercommunicatively coupled to the positioner and configured to generate oneor more control signals to which the positioner is responsive to causethe positioner to irradiate the workpiece according to a scanningtechnique to deliver at least one laser pulse from the beam of laserenergy to the workpiece to form a via in the workpiece, whereincharacteristics of the beam of laser energy and the scanning techniqueare such that laser pulses delivered to the workpiece: a) vaporize afirst region of the dielectric structure at the surface, therebygenerating a high-pressure region between the first region of thedielectric structure and a first region of the electrical conductorstructure, and b) heat the first region of the electrical conductorstructure such that at least a portion of the heated first region of theelectrical conductor structure is ejectable from the workpiece by thehigh-pressure region.
 18. The apparatus of claim 17, wherein the beam oflaser energy has a wavelength in the visible green range of theelectromagnetic spectrum.
 19. The apparatus of claim 17, wherein,according to the scanning technique, at least one laser pulse from thebeam of laser energy is delivered to the same location on the workpieceto form the via in the workpiece.
 20. The apparatus of claim 18, whereina plurality of laser pulses from the beam of laser energy are deliveredto the same location on the workpiece over a time period in a range from1 μs to 30 μs.